It's hard to say which is best as the top 3 have different styles and different attractions.
For example I myself love EPL the best despite La Liga/Serie A having more skillful players and flair players like South Americans.
But then EPL has its own great things like direct/fast paced style of game like ClassicD said, the crowd, the atmosphere the intensity and the fact that at ALL times it looks like everyone is giving 110% where as Serie A sometimes I watch some lower teams and they look like Primma Donnas and some aren't even giving 90% you see them walk back instead of sprint back and not dive into tackles with same passion/intensity that they do in Germany/EPL.
So It's very hard for me to say which is best league and each have their own reason for keeping me attracted and a frequent viewer but all I can say is the top 5 leagues are definately:
EPL
Serie A
La Liga
Bundesliga
Ligue 1
and then after these 5.. for those who really follow football and aren't just talking crap you can see quite a large gap between 6th championship and Ligue 1. Whehter that's Eredivisie, Russian league, Turkish or Portuguese Superliga.. Ligue 1 is MUCH MUCH better than them in terms of quality/players and even-ness of teams where anything can happen and there's many descent teams who can finish anywhere between 15th to 6th in France while in some other countries like Scotland, Portugal, it's same story of big 2 or big 3 clubs and veyr boring.
Now I know Lyon has won 4 times in a row.. but it's been an exciting race and involving different challengers each time once with Nantes, Lens won it a few years back and then once PSG coming close and once Monaco.
For me Ligue 1 and the other top 5 are all great leagues that I just have to watch and follow and it is football at its best and the gap between 1st league and 5th league is actually NOT as much as English/Italian and Spanish think. They often really under-rate Bundesliga or Ligue 1 where as quality of those leagues is also very high and so are the players which is why you see a shit load of French players in each EPL team some even coming from lower teams like Rennes to teams like Chelsea or even from 2nd division like new Chelsea youngster Diarra.
Anyways.. so this is a a never-ending debate one can have over who's actually 1st, 2nd or 3rd but I don't realy care bout that and there is no real ANSWER. Comparing how Italian/Spanish and EPL teams faired against each other is not the be-all, tell-all. What about how strong all teams are???
In france for example.. teams are very close to each other in terms of squad skill except few teams who are better like Lyon/PSG/Marseille who have bigger budgets and this makes for a very intersting season every year as each year there is a team that pops up and breaks into first 3 or so last year it being Lille, few years back Nantes did and won the league, year before that Lens did and won the league and also teams like Auxurre doing it sometimes and seeing Marseille near last is always fun

and not necesarily something you see in other leagues because over there the gap between top teams and rest of league is TOO MUCH.
Fact is all these 5 are highly entertaining, high quality football and I'd hate to miss out even on a single one and it's very tough deciding which is actually #1 #2 and #3 because all have their good/bad points.
After these 5, being a football freak I obviously still like to follow Turkish/Russian/Holland and Portuguese as well as Brazilian and Argentininan league to Some level.. but it's not a MUST for me like the top 5 leagues cuz those are the SHIT!
