Driving

I'd suggest using the ViaMichelin.com website or their smart phone app. It'll give estimated time, mileage and costs. You can also opt for various routes.

One answer to the discrepancies is that each leg has a choice of routes. Or maybe the books are not very good! Make sure the car has a full tank of fuel when you collect it. The plan looks sensible (actually some of it is in an itinery I have planned for September!!)

Day 1. Airport - Oban assuming it isn't peak commuting time around Glasgow. Both routes cross the river on the Erskine Bridge and head alongside Loch Lomond, they would both take about 2.5 hours without breaks but I doubt very much whether you could manage not to stop somewhere! Beyond the village of Tarbet you can go either way.

Left takes you down to sea level and the village of Inverary which is worth a walk around. Then via A819 onwards. Note village and parking is beyond the A819 intersection so don't turn if you want to visit, carry on and come back afterwards! A819 is a nice drive and if you pay attention about 14 miles after Inverary there is a stunning view of Kilchurn Castle on the left (subject to weather). At the end of the A819 turn left onto A85 (everything is well signposted).

Right at Tarbet takes you north into higher ground with views into some serious terrain, although the road is a good one so nothing to worry about. After the village of Tyndrum you turn onto the A85. The villages on this route are not a pretty as Inverary but the scenery is good.

After the A85 passes the end of the A819 both routes are back together and just half half a mile later you should pull off into a small road on the left. This takes you to the parking area for Kilchurn Castle. It's all free of charge, you've come all this way, it would be insane not to visit (unless it's raining hard in which case teh access may be flooded!)

https://www.historicenvironment.scot/visit-a-place/places/kilchurn-castle/

after that you just go back to the main road, turn left and keep going all the way to Oban. As I said, 2.5 hours driving but allow 4 - 5 hours with stops!

Day 2. You are looking at at least 4 hours driving plus some added time. Leave Oban the way you entered and just before Connel Ferry you turn RIGHT (sounds wrong, on a basic map it looks like a left). Take A828 to Fort William. You climb a little to get onto the bridge. The road to Fort William spends much of the distance following the shore line. At Ballachulish cheap maps suggest you turn left, but you actually go beneath a large bridge, continue a litle way and then meet the A82, then turn right and climb up onto the bridge. Eventually you reach Fort William which has any facilties you may be needing but isn't that pretty. At various points on the right are views of Ben Nevis which is the highest mountain in UK.

After Fort William there are 2 choices. Just before the Ben Nevis distillery (and visitor centre)
http://www.bennevisdistillery.com/
there is the intersection with the A830 to Mallaig. This road runs via Glenfinnan with it's famous (thanks to Harry Potter) viaduct plus the monument to Bonnie Prince Charlie. The road mostly follows the railway where you may see the Jacobite steam train http://www.westcoastrailways.co.uk/jacobite/jacobite-steam-train-details.cfm

after Arisaig there is a road on the left signposted Back of Keppoch which runs near to teh sea with better views. This is the area where movie Local Hero was filmed (Burt Lancaster's oil tycoon fell in love with beach etc..), the road loops around and comes back to the main road.
From Mallaig you need to take a ferry, which can involve a wait of around an hour depending on how lucky you are with arrival time. https://www.calmac.co.uk/mallaig-armadale-skye-ferry-summer-timetable

If you don't want the ferry ride go north at Ben Nevis distillery and go left at Spean Bridge to stay on A82 until you reach A87 then go left, this is pretty wild scenery with few villages until you get back near the coast and Kyle of Lochalsh, this used to be a ferry crossing but now has a bridge over to Skye and on to Portree.

Either route has around 4 hours driving but the ferry (and waiting for it) is an unknown, could add anything from 30 minutes to 1.5 hours. Plus any other stops.

Day 3. This depends on day 2. If you used the Mallaig ferry there are 2 choices to Inverness, but one is a rerun of the A87 so if you came this way don't use it. Go back through Kyle. There is a road on the left A890 signposted Loch Carron, if you used the A87 on day 2 take this road for a change. But 3 miles beyond on the A87 is http://www.eileandonancastle.com/ which is worth seeing whichever route you intend taking. The A890 crosses over to more coast and hills and several little villages until it meets the A835 at Garve where you turn right. This road enters Inverness from the north merging with the A9 and crossing over the Beauly Bridge.

If you use the A87 route go straight ahead when the Fort William road turns off. You come down to Loch Ness at Invermoriston. The signposts say turn left on teh A82 but this road has a reputation for heavy traffic. So you could turn right, go down to Fort Augustus and then left onto B862 via Foyers, this road follows the east side of the Loch and is much quieter. Either side of the Loch you entre Inverness from the south.

Either route 3 hours driving plus stops. If you took the A890 but really want to see Loch Ness (monster no guaranteed...) you should have time to continue on from Inverness, exit past Bellfield Park on B862 and follow signs to Dores, you should reach the side of the Loch in about 20 minutes.

Day 4. The obvious route to Edinburgh is down the A9. Which is why everyone else will do it! We do as far as Aviemore but here the old and quieter road becomes a viable option with less traffic. Go past the town then turn left A9152 Kincraig. This road follows the A9 but with less traffic until Newtonmore where you rejoin the A9.
If the weather is clear you could visit the Cairngorm mountain railway (follow brown signs from the A9152 turn off). http://www.cairngormmountain.org/funicular-railway/
This will be a 3-4 hour diversion from the journey but worth doing if you are in the area in good weather. Afterwards come back to Kincraig and Newtonmore.
South of Newtonmore the road is quite busy with various towns plus Perth which is much bigger and really needs a few hours to see. Beyond Perth take the M90 and the passenger should have camera ready! After the Dunfermiline exit you may run into some roadworks (hopefully they are all but done), where they are preparing to divert the road. You will go on to the Forth Road Bridge of the 1960s, this is closing to most traffic at the end of August. On you right is the brand new replacement, on your left the world famous rail bridge. You cannot stop on the bridge to view them but at the south end of the bridge there is an exit to Queensferry which takes you down into the old town below the bridges and you get good views from the quayside.

If the car needs to be at Edinburgh Airport, or you are going to the south side of the city take the M90 from South Queensferry. If you need to go to north side or city centre take the A90. (why won't this board let me put single letters in bold???)

The driving time for this day will be 4 hours but you could spend as much again on stops.

Before you leave Glasgow airport, ask the rental car agent which signs to follow at the roundabouts leaving the airport to get on the motorway headed toward the Erskine bridge. The signs are not self-explanatory and there's more than one roundabout, as I recall. If you find yourself on the M8 headed to Glasgow and Edinburgh, you're going the wrong way.

Along the western shore of Loch Lomond you could stop and take a cruise on the loch. Cruise Loch Lomond operates out of the dock in the scenic village of Luss.

Between Portree and Inverness you'll be driving along the northern shore of Loch Ness. Stop at Urquhart Castle and the Loch Ness Centre & Exhibition. Two very different experiences, both well worth the stop.

East of Inverness are Culloden Battlefield and Cawdor Castle (with a herd of highland coos). You could continue eastward and have lunch in Nairn, enjoy the scenic beach there before returning to Inverness.

meanwhile the news from Skye.......

http://www.bbc.co.uk/news/uk-scotland-40874488

A good rule of thumb, at least from my experience there last summer, is that it always takes longer than you think it's going to.

Thanks to everyone for their posts. It was a great trip and the driving turned out to be fine. 😀

Did you use the Mallaig ferry and if so did you reserve space or just turn up? Others have been querying this in other posts.

While we were eating lunch at restaurant in fort William we checked for reservations. No dice. We used the bridge. Easy