Apparently most people have an actual numerical ranking? I don't really have a precise ranking, though I do sort of group the books mentally.
-TDR through LoC are my favorites, with plenty of action intermixed with enough breaks for character development, but while still having sufficient character viewpoints that even the minor characters actually have import. I'd say TSR is my favorite among these, but I love all of them.
-EoW and TGH are solid, but you can definitely tell that RJ was still sort of figuring some things out, both stylistically and in terms of the world, limitations of the magic system, etc. They're interesting, but I always get a bit of an unpolished feel whenever I read them.
-WH and KoD through AMOL all have their moments, but also have notable flaws. I still enjoy reading them though.
-CoT, PoD and to a lesser extent CoS: Blech. When I reread the series recently, I pretty much skimmed over these. I'll be fair and say I understand RJ's intent that "the Dark One's touch on the world is making things sort of freeze in place and slow down". I just don't think it works. Honestly, I actually think some of the legit criticisms people have of the way AMOL wrapped things up (e.g., ultra-fast pacing, lack of character reunions, many minor characters essentially vanishing, Moiraine) were heavily rooted in the fact that there's little to no action for like 1,500 pages in the middle of the series. Absolutely, BS could have written AMOL better, but there was just way too much left to "hey this needs to get handled before the Last Battle" that caused issues.