Itinerary advice and which day trip from Glasgow?

You don’t need to do a tour from Edinburgh to St Andrews. It is easily done by bus
https://bustimes.org/services/x59-edinburgh-st-andrewsfrom Edinburgh or by train to Leuchars and then bus to St Andrews.

Falkland isn’t as easy (I’m hoping isn31c can help out here...) If it is visited on the Outlander tour that makes life a lot easier.

As far as the day trips from Glasgow are concerned, that is a difficult decision. It may come down to how important it is to see Glenfinnan viaduct. Tour 1 looks like an out and back along the same route. Both Tour 2s cover the same out route between Glasgow and Glencoe but do have the advantage of doing a loop round by Oban, which would let you see a bit more scenery.

A lot may depend on whether you want to see Glenfinnan or more scenery.

My family and I did #2 with Rabbie's a few years ago. It was a very good tour, with a great guide (who told us a great deal about Jacobite history) and a well chosen variety of sites and beautiful scenery. I wouldn't worry too much about not enough time in Glencoe. Glencoe is a tiny village. Unless you're a hiker, which you won't have time to do on any day tour, pretty much the only thing to do is admire the view, which is indeed lovely, but it doesn't take long to do that. It would be unfortunate to do this tour on the day Inverary Castle is closed, as that was one of the highlights, but I think it still would be worth doing. Perhaps they will compensate that day with a bit more time in Oban, which is a town I liked a lot. That was the lunch stop (on your own) and there was time as well for a quick look round, but would have liked more.

I think you're going to be sorry not to have more time in Glasgow for Charles Rennie Mackintosh architecture. I'd plan a very late train to Edinburgh on Day 4 to allow more time in Glasgow.

I took the Discover Scotland tour of Glenfinnan Viaduct, Glencoe & Loch Shiel this past June, and it was one of the most memorable days of my 6-day trip. Yes, it was a long day--especially since I took the tour departing from Edinburgh rather than from Glasgow--but it was not just endless hours on a bus. We had ample time (hours) to explore the two main sites, Glencoe and Glenfinnan/Loch Shiel (the viaduct, the Glenfinnan Monument, and the loch are all at the same stop, with just a short walk between them). Glenfinnan is indeed stunning, and Loch Shiel is jaw-droppingly gorgeous. Needless to say, Glencoe is also very beautiful, and we made a short photo stop as we approached it, as well as a much longer stop at the Visitor Centre. The tour also included short "rest stops" in Callander (at the Trossachs Woolen Mills) on the journey out and in Pitlochry (on the main street) on the way back, which gave us additional chances to stretch our legs, take pictures, and meet some cows. :)

My trip report includes more details in case you're interested: https://community.ricksteves.com/travel-forum/trip-reports/trip-report-6-days-solo-in-edinburgh-in-late-june-2023-with-day-trips

When I head back to Scotland this coming May (same month you're visiting!), I am planning to take Discover Scotland's Highland Lochs, Glens & Castles tour from Edinburgh. It covers some of the same ground as the #2 tour from Glasgow that you're looking at, but doesn't include Glencoe or Oban. It does include Inverary, and, after reading lots of reviews, I decided that I don't absolutely have to take the tour on a day when the castle is open. Only a few rooms are open to visitors, and I think I'll be satisfied with touring the gardens and grounds.

Thank you both for your thoughtful comments! I’d prefer to go to St. Andrews on my own, but was hoping to see both Culross and Falkland. When I planned my original trip for 2020, there were a number of Outlander day trip options that included both, but the 2024 itineraries only visit Culross. I may wait to book a St. Andrews/Fife tour until I’m there and can see how the other day trips go, since I can always go on my own if the tours are full.

That’s a good point about tour 2 covering more scenery instead of up and back on the same route. The longer stop at Glencoe on tour 1 includes going to the visitor’s centre and turf house as well as the photo stop, but I’m not sure how much is at those locations? It’s helpful to know that a quick stop there may be enough.

Acraven- thanks for the suggestion! I’m not planning anything in Edinburgh that day so could certainly stay in Glasgow until later. I’m planning to visit the Mackintosh gallery at Kelvingrove as well.

NancyG- I did read your tour report and am glad you enjoyed the day trip! Helpful to hear it wasn’t too much time on the bus. The tour you’re doing this year looks wonderful as well, I hope you enjoy it!

Re-Falkland Palace you would take the X59 as far as Glenrothes- https://bustimes.org/services/x59-edinburgh-st-andrews (for some reason which I can't fathom Wasley's Link above for the X59 isn't working as it should).
At Glenrothes change to the hourly 36/36A to Perth (20 minute ride)-https://bustimes.org/services/36-glenrothes-bus-station-perth-bus-station?date=2024-01-03&service=71010

or the 2 hourly #64 (to St Andrews, run by Moffat and Williamson)- https://bustimes.org/services/64-glenrothes-st-andrews

So plan your day and you can see both Falkland and St Andrews.

Glenrothes itself is a modern new town but the bus station is a major interchange point for buses in the area.

If you get a Stagecoach East Scotland day ticket (£11 last time I looked) that would cover both rides (X59 and the 36)- it covers all Stagecoach local bus journeys between Glasgow/Edinburgh to Fife, then Perth and as far north as Aberdeen.#

By the way the X59 is a quality coach-bus with an on board restroom, air con, leather seats etc. It isn't a city bus.

This is incredibly helpful, thank you so much isn31c! I will definitely look through the bus schedules and see about timing options for visiting Falkland and St Andrews on my own.