well, i've used both P's and J's myself. other than the first walker 7" i did back in '94 where i used a MIM P, everything else i recorded over with that band was with the MIJ '75RI Jazz i mentioned in my previous post. but live, i would occasionally break out a MIA P, but not often. i've found that more often than not, the kind of bass used in pop-punk bands partly depends on how "active" the bass lines are. Bands like Anti-flag or Squirtgun where the basslines are all over the place will be more likely to have J's, whereas the typical "Ramones" influenced bands who's bass players more often than not just follow the root notes will normally be using P's. of course there are always exceptions, like Mike Dirnt who's been pretty much consistently used P's since he ditched the Gibson Ripper. and as for the P/J, I've seen Matt Freeman use one live a couple of times over the years, not sure if he ever used one to record. but anyway, yeah, just try a bunch of different basses and find what fits your playing style and sound. if you like the sound of a P, but prefer a Jazz neck, get a P/J or do a custom by getting a P body and J replacement neck.