I've actually been shopping for a set of mud terrains for myself these past couple weeks. Just like you, I currently have ATs and wanted to change to MTs. And I literally JUST picked up a set this morning.
Through my research, I used a few sources to compare the tires with.
Offroaders.com is a site that has reviewed dozens of MTs & ATs, they do their own personal reviews for the site as well as a forum where users can contribute to reviews as well
Main site for reviews:
Off Road Tire Guide for Mud and All Terrain Tires - Offroaders.com
User generated reviews:
Reviews - Mud Tires, MT, Aggressive Tread Tire Reviews Reviews by Offroaders.com - - - - - - - - - - - - - - - Review Engine Powered by ReviewPost
FourWheeler.com has also done a lot of comparison articles for MTs & ATs, here are the 2 longer articles they've written for tire comparisons
Off Road Tire Performance Guide - Jp Magazine
The Hot Sheet: 33 Off-Road Tires Tested - Jp Magazine
And finally, TireRack has a comparison chart for MT/AT tires with customer surveys
http://www.tirerack.com/tires/surveyresults/surveydisplay.jsp?type=ORAT
as you know, not all tires are made the same, some are better at certain terrains than others, so you really have to figure out what terrain suits your driving habits best. I daily drive my car and it stays on concret 90% of the time so having good on road performance was my number 1 priority. Followed my tread life, price, and of course all the other terrains, I ranked myself from most to least important: Snow, Trail/Dirt, Sand, Mud, Rocks.
Having said that, I dwindled down my choices to:
GoodYear Wrangler Kevlar MTR
Hankook DynaPro MT
BFGoodrich T/A Mud Terrain KM2
Nitto Trail Grapplers MT
Toyo Open Country MT
I ultimately chose the Hankooks, they were rated as a very good all around mud terrain that performed very well on the street and they were priced much cheaper than the other 4 options. The other 4 were all in the 280-330 range per tire while I found the Hankooks for $225 a tire. The one knock on them was people found them sometimes difficult to balance and that they wore off fairly quickly, but I don't drive much so I feel like I can get a good amount of life on them as long as I rotate them regularly. As for the balancing issue, it seems like it was an issue thats been resolved as I noticed the reviews mentioning that dated between 2007-2010, havent seen any recent issues regarding that.
Also, the Hankooks won in a mud terrain shootout from FourWheeler.com, beating out 3 of the 4 of the other tires I mentioned (no idea why they didnt have the Toyos in their rankings). That was probably the last article I read that finally convinced me to get them.
Mud Tire Shootout First Place: Hankook Dynapro MT - Four Wheeler Magazine
And for reference sake, here's
FourWheeler's top 10 rank in their MT shootout:
1. Hankook Dynapro MT
2. Good Year Wrangler MT/R with Kevlar
3. Mickey Thomson Baja MTZ
4. Nitto Trail Grappler MT
5. Yokohama Geolandar MT
6. Pit Bull Rocker LT Radial
7. Interco Super Swamper TrXus
8. BFGoodrich Mud Terrain T/A KM2
9. ProComp Xtreme Mud Terrain
10. Maxxis M8060 Trepador
Ultimately, you really can't go wrong with the 5 tires I picked, they're all from companies with great reputations and all make a quality product, they all have their pros & cons, but theyre all great all around tires compared to the dozens other out there that are cheaply made.