I've probably done about 100 of Druidh's 283 munros with him – so I can answer for him if you like 🙂 He would say "do the Tarmachan Ridge".
Schiehallion is a nice place to be on a clear day due it's uber central location and it has a nice "real mountain" feel with no navigational challenges.
Ben Lui is a classic hill, although I've only done it from the Oban road – the gully route from nr Tyndrum is the nicer route when you don't want to link it with it's neighbouring munro.
Stuc a'Chroin from near Callander is a nice short drive, an easy walk and gives a really nice/unusual view of the highland boundary fault.
Lochnagar would be a fantastic walk (I still might be saving that one for my final munro) and there are lots of others from nr Braemar which is within your 2 hour limit…
Edited to add: I started that before I read Glen's post – must be of a similar mind…