I personally think Wenger is the best...sure there haven't been the trophies in the past 6 years (though there were a lot of injuries and bad luck along the way, and they've been so close so many times, especially the Champions League final against Barca), but when you take in to consideration the amount of consistency he has had, the football he plays, and the future he has set up Arsenal for (look at how young their squad is, they will be great for the next several years) with the budget he has had over the past several years is truly remarkable.
If you look at the other Premiership clubs, they couldn't maintain the consistency. Liverpool was usually not as good as Arsenal, even if they got a couple of trophies, and they spent tons of money and ended up falling out of the top 4 for a couple seasons and having to seriously rebuild their squad. Chelsea, sure they won more than Arsenal, but they lived in a fantasy land because of their rich owner, and they have a core group of really old players. They might fall out of the top 4 this year and have to spend tons of money rebuilding their squad for the future. ManU? They're the biggest club in England with a great manager, and they had unlimited funds for many years as well as a great youth academy that churned out some great players. But look at them, they may not be sustainable, either. They have tons of big shoes to fill: SAF, VDS, Ferdinand, Giggs, Scholes, etc. I don't think their current crop of players, Carrick, Park, Valencia, Berba, O'Shea, the twins, etc. are in the same class. They will have to spend a lot rebuilding the squad, and Ferguson will probably leave right very soon, right when this happens. The next manager will have a hard time I think, and it'll be awhile before they have the success of the previous era.
SAF is obviously also great but I think Wenger is just as good. I don't think anyone could have done what he's done with Arsenal on that budget, and the future is very, very bright for that team. I think they'll be the dominant team in the Prem for the next 5 years, and had they avoided some terrible results (Newcastle, that 0-0 draw with ManCity, the draw with Sunderland, the last minute goals, the CC final loss, etc.) they could have won some trophies this season.