Personally, I think the latest update on the Market Wards solved the majority of the problems I was having.
I can now find the items I want without spending days running around hopping I get lucky.
I only have two problems;
1) There's not a sort feature for armor by level, stats, etc. within a search page.
For example;
If I'm looking for good leg armor, it's hard to figure out what is better for me without scrolling up and down the page listing every leg armor.
2) Most of the wards make sense now....but only 3 separate wards for most of the armor groups makes it hard to track down what level range lays in which ward.
Personally, I'd like to avoid an AH if at all possible.
To my knowledge, a main reason against an AH is the fact that RMT can 'read' it, get character's names, then spam them in /tell. This got annoying when I played FFXI, and I know it really gets to some people.
Another is the fact that inflation of the high-demand items will skyrocket. Right now, everyone lowballs everything a bit because it's hard to figure out how much gil is a lot gil. With the wards system, there's nearly always someone selling something cheaper than someone else and if you're quick you can get a bargain!