I've attended a game (or multiple games) at every SEC stadium, and Neyland is nowhere near the top.
Yes, it's big, but it's a horrible fan experience. First of all, one of their "additions" of 10,000 seats was accomplished by re-painting the bleachers so that each person has less room. As a result, you're packed in like sardeens.
Next, despite all of the seats they have, their concourses are tiny. I actually spent the entire halftime just trying to traverse a quarter of the way around the stadium to meet up with a friend. And their restroom facilities are poorly proportioned as well.
Finally, the stadium is of the old "erector set" steel variety. When was the last time you saw a new stadium built that way? Concrete is more aesthetic, more stable, and holds the noise in better.
That said, I'd rank LSU #1, UGA #2, UF #3. If you count pre-game festivities, Ole Miss is right up there.
I'm a Gator fan, by the way, if you're wondering.