I think I'm leaning towards the SRAM. If I didn't have choices, I'm sure I'd be fine with whatever - as long as it works. The Shimano was fine. Then I tried a bike with SRAM and it, too, was fine. Now I have a decision to make. The SRAM seems to work like the rapid fire shifters on my other bike. Repeated clicking to move more than one gear, so maybe that's why the transition doesn't seem difficult. Thanks everyone!