We've had a couple of coach trips, but for specific events, a long weekend really, and they weren't too bad. I'd be very wary about a trip to Scotland, a long way up and back, and as several have said, only a part of the time is your own. (Did you mean a tour from way down in England?).
The last time we went to Scotland, we flew to Edinburgh (from Brum), got the bus into town, picked up a hire car, then had 3 days in the borders and 3 around Edinburgh and nearby. It was lovely.
I just Googled coach tours from Glasgow or E'burgh, plenty of choice, Discover Scotland looked interesting.