Which train station in Glasgow is the best place to pick up a rental car. We would be taking the train from Edinburg to Glasgow and then heading up to Glencoe or FortWilliams.
If you are hiring a car it's hardly worth taking the train from Edinburgh, you may as well get the car there. Centre to centre is less than 50 miles, would cost about £6 in fuel and nothing extra on the rental. Either go all the way by car or all the way by train.
Agreed -- if you are already going to be in Edinburgh, pick up the rental car there and drive to Glencoe or Fort William (only one William, not plural Williams). OTOH, if you wish to spend time seeing the sights of Glasgow first, then it could be a good idea to travel there by train from Edinburgh so you wouldn't have to deal with parking or with navigating about city streets.
From downtown Glasgow I believe there is frequent & convenient bus service to the airport. I can attest that picking up a rental car from Glasgow airport puts you right near the Motorway, but you have to go through a couple of roundabouts with non-obvious signage on your way out of the airport. Ask the rental agent specifically which signs to follow to get on the Motorway toward the Erskine Bridge and Loch Lomond.
There may possibly be a good place to pick up a rental car in Glasgow city centre, but I'm not sure where.
There are hire car centres on the outskirsts of the city. There is one just north of the M8 for Enterprise. It is worth contacting the companies in question.