I jump between all 3 regularly. I have no problems using either, but find they have different advantages (for me) depending on the riding. For DH/DS/4X, where time is money, it's grip shift all the way. I like being able to go through the block (up or down) NOW. I use full size Renthal PWC grips, and have no problems sliding my thumb and finger over to shift while still gripping the bars. For jumping. aggressive trail, and mucking about where you need to make one or maybe 2 shifts without much effort RF works good for me. Leisurely trail and pooting about I like the simplicity of thumbies, and the fact that you can trim the front for silent operation.