I move around a lot during most of my smoking time and while I have many different #'s in the Peterson line that serve many variable purposes, my preference is a 314 with a P-lip for my favorite all-'round. It moves well with me, hangs well for my purposes, and has the chamber size that suits my palate taste / length of time per bowl preferences in general. I have several.
Systems are made both with and without P-lips, in "standard" and 9mm / filter styles. I haven't purchased any 9mm... I have both materials of stem and they both perform similarly to me.
Overall I have become a fan of the system, and the 1 or 2 I have that are "premier" seem to perform a little better overall than the "standard", but I don't mind standards at all.