Only thing I don't like about my 29 is the availability of good factory ammunition. Most offerings are loaded pretty mildly, but you can find something hotter. Just be prepared to order it or have a local store order it for you.
The 29's size is convenient and recoil is manageable. No firsthand experience with the 20, but I'd imagine it's easier to shoot. My pinky hangs off the bottom of the 29 (nothing an extender couldn't fix).
