Prestwick have always been fine in my experience. Don't bust a gut to avoid them for the sake of it.
Oban.... you couldn't choose a nicer place to go to if you tried. Paul Keegan, the airport manager is one of the best.
Loads of decent places to go to nearby ranging from the pub at the foot of the Bridge over the Falls of Lora through to various places in town.
If you decide to stretch a point and stay overnight, I would heartily recommend the Lerags House Hotel. You'll find the details through Google.
PM me if you want more details. I have no commercial connection to any of the above, but I am a huge fan of Oban (if you didn't guess)
2D