At this point I highly recommend webapp2. Most tipfy features were
ported to it.
An important point is that webapp2 is compatible with webapp, so you
can use all App Engine docs and webapp examples with it, and current
(and future) SDK handlers will work out of the box with webapp2. Also
Google plans to include webapp2 in the SDK, so it is definitely a good
bet for the future (this is extra-official, don't quote me :).
-- rodrigo