My advise is to rent a car, don't take the bus tours. You will find many excellent places off the beaten path. You can still hit the high spots like Stirling Castle, etc. Take the single lane roads and you will find many jewels that only the locals see. Single lane roads take driving on the wrong side of the road worries away haha.

Stay in B&B's, all the ones we stayed in the owners are very helpful and gracious host.

I personally like the west coast, highland country, but that is personal preference.