There is no doubt in our mind that the best way to travel to Riva is by Sita Bus. We were most impressed by the drivers, the cleanliness and comfort of these buses.
The ride is smooth, you sit high enough to see over the growth on the side of the highways, and you may choose to hop off as you enter a village you like the look of. If you purchase a ticket to the furthest destination, it is at the discretion of the driver whether or not to accept your ticket if you get off before your destination, and attempt to board a later bus to continue your journey. Perhaps tickets specifically for this purpose are available. I'll try to find out.
Sita bus stops are usually found at two or three places along the main highway within larger towns, often in the town centre, near a group of hotels, and on the outskirts. Use caution if you plan on travelling during off seasons, as service is lighter than usual. Expect too, that buses might be full if you travel during peak season.
Ok, this is something you might already know, but we kinda forgot all about it: there is no shortcut through a mountain!
So after many hairpin bends and breathtaking views we had to make a 180 degrees turn and have an opposite look at the mountains.
Ah well, since I had taken lots of photographs already, time for me to have a good look. ;-) at our surroundings.
You can get to Riva del Garda by the bus from Trento, Roverto, and Verona. I took the bus from Trento which costed 3.20 euros one way per person. The buses are air conditioned and are comfortable. The buses take the small, steep mountain roads -- but don't be afraid. The driver of the bus is very skilled.