pace, spirit, fans, stadiums - the prem. negatives are tactics and an overall lack in terms of skills. most of the tactics is extremely defensive or blind offense. it's very rare to see a team with a two dimensional gameplan.
open games, top level skills - la liga. every team has at least two or three players that would walk into any prem team skillwise and the public demands attack. negatives are an at times naive approach to competitive football (covered up by some talented footballers).
tactics, overall skill, competitiveness, coaches - serie a. although they're not the natural central gravity point of the football world anymore in terms of stars, you rarely see a footballer who's not competent. all the gameplans are sharp and competitive (except for romas by default) and even a team like chievo will take some serious thinking before slippin a ball through the defense. the negatives are the lousy stadiums, the poor tv-productions, the fed up/bored fans and slow pace (the latter because serie a teams rarely drop 2/3 of the pitch like most prem teams do).
if i were to rate them i would place serie first in terms of "elaborated" football, the prem for spirit and la liga for entertainment.
and all of them have their own charm.