The Pietenpol has a large and vibrant builder community, but there is certainly no shortage of Cub fans and expertise out there as well. As was already mentioned, unless you go with the welded steel tube Piet fuselage, the biggest difference is the steel and welding requried with the Cub. There are also workshop size issues as the original Piet' has a single 29' long wing, though there is an optional three-piece wing. I personally I prefer the open-cockpit ambiance and working with wood, but a Cub is certainly great fun.
Assuming you are looking at two-seat, low-and-slow, high-wing designs, here are a few more to consider:
--Pober Junior Ace (side-by-side open cockpit, wood parasol wing, steel tube fuselage and tail, plans)
--Fisher Flying Products Horizon 1, Horizon 2 (Cub- or Cessna-like high wing, all wood, kit or plans)
--Christavia Mk1/Mk2 (tandem/side-by-side) (steel tube fuselage and tail, wood wing)
I won't go into all the single-seat possibilities, but I should, of course, mention Eric Clutton's FRED, since that's my site! Good luck and let us know what you decide.