I've been to all of the stadiums in the SEC, having been to most of them a few times each.
Tennessee is number one for road stadiums in the SEC. Taking away personal feelings and just focusing on the atmosphere, traditions like the Vol Navy, Vol Walk, the band marching through campus to play to the hill, the stadium itself (despite the bad, small seats), the team running through the 'T", the halftime shows...it's hard to beat.
LSU is great, too. I've always eaten for free there (not sure what some it was...), the campus is nice, it's loud. Great atmosphere.
Georgia has it all -- great campus, cool college town, nice stadium, and the rudest fans of any school in the conference. That's what sours it for me and makes me never want to go back.
Florida is right up there -- loud, interesting stadium, great campus.
Underrated are probably Mississippi State and Arkansas. Both nice campuses. Arkansas, once you get there, is a great campus and the stadium has come a long way. Fayetteville is a neat college town.
As far as non-conference venues, I've been to Ohio State, Notre Dame, Michigan, Georgia Tech, Florida State, Purdue, Penn State, Navy, Boston College, Ohio University, Troy and UAB.
Ohio State was easily the wildest (it was Michigan week). I love old stadiums and the horseshoe was awesome. Kegs and Eggs at 6:00 am on game day -- nuts....
Notre Dame has the tradition. Like it or not, it's a different feel there than anywhere else. I could feel the history there with each step. The band marching through campus chanting "Here Come the Irish." College football is more fun when Notre Dame is good.
I like Georgia Tech. I haven't been since the expansion, but a nice campus tucked away beside downtown Atlanta. The Varsity. The Budweiser song at the end of the 3rd quarter.
Florida State -- the stadium used to be a dump. Then they renovated, and it is truly impressive on the outside. I got to go to the Golden Chiefs hospitality area, which is nice, so that probably sways my opinion.
Penn State -- fans with as much class as any around. They were that way when we played them in the 70's and 80's. I saw them play in Happy Valley in probably the coldest game I've ever been to. They lost to Iowa 21-20, and I'm not sure a single fan left the stadium before the game was over. It was sleeting, raining and just plain miserable. I hope I can make our game up there.
Most disappointing -- Michigan. It was definitely a wine and cheese crowd. Saw Northwestern beat them the year they went to the Rose Bowl. That would've been like Vanderbilt beating us. The crowd did nothing to help push the team, as they were in a dogfight. They didn't seem to be too upset about it. Our fans would've tried to fire our team up. Theirs did nothing.