All depends on what you are doing, bashing or racing, if racing the only real option is the Samba pipe, quiet and good on low end, but does lose a bit on the top end, if bashing, the original Bartalone pipe is good, but a bit frail where it is bolted onto the engine case, mine was always working loose and losing the alloy spacer, the Bartalone Xp bigbore solves all the fit issues and is a really good pipe, but bugger me it is loud, can't comment on the jetpro's as have never seen a 5 with one on, also the Bzm micro pipe seems to work well.
The biggest trick with the five is to keep the clutch cool, crack that and you will have good pickup and top end that will last.