Which chapters have you been to? Most of my visits were in the 90's. I've been to:
Oklahoma - They used to be HUGE till I think they got in trouble for hazing or something. I went down there as a pledge to help them with rush. They were pretty badoff and needed mucho help with getting numbers up. I stayed friends throughout college with some of them. Very nice guys. The house was one of those monsters built solely to house bodies. I think it could sleep like 80 or something. It wasn't very good looking tho. (@ around 35 members as of 2006)
Oklahoma State - I've been to this chapter a few times. They have always been HUGE (well over 100). The house was VERY nice I thought. It is on a very good corner, right across from campus. They seemed like good guys from what I remember. (around 130 members as of 2006)
Arkansas - Their house kind of reminded me of OU's house. Built to house many bodies. Not very impressive, but I think it is gone now as they are building a new one now that they are back on campus. Don't remember much about them; but I do remember getting stopped near the bar area by cops, they asked where we were going and when we said "Sigma Nu" they were VERY nice and gave us a lift. I think one was an alumni. (I think they are at around 80 now).
University of Central Arkansas - Not sure why we went there, but it was right after they got a charter. VERY good guys, and they had a nice party with a lot of hotties. Good ol' country boys for the most part.
Kansas - Their house was the old governors mansion. I got a nice tour of it, and came away VERY impressed. One thing I remember specifically was they had composites lined up on the walls all around their huge dining area, and I swear they had them back to the 1800's. Dont' remember much about the guys. I think they were also well over a hundred members then. I remember thinking it was very cool that all the fraternities and sororities on that street had a "SIGMA NU PLACE" address.
University of North Texas - My gf at the time went to grad school here, and I remember going to visit the snake house once. The guys were very nice and the house was pretty pimp. Classic mansion style with columns. (60-ish members I believe)
UCLA - We roadtripped to LA, and Mexico one spring break. I think UCLA was still in school so we stopped by the house. It was like a Tuesday and they were having beer relays or something. It was a blast. Very good guys, I seem to remember them all being big ol' boys. Guess they had a nice weight room or something.
House was very nice and big. Not sure of the style, but it wasn't the classic mansion look. It was huge tho.
Arizona State - Same trip as above. HUGE house built like a tank. Swimming pool that gives them an advantage over everyone. You can tell they are the Big Men on Campus. Closed down - Risk Reduction Violations (hazing I believe). Back on Campus as of '04. (87 members as of 2006)
TULSA - My chapter. Our house was terrible looking. Built in the 50's in single level style that was popular then I guess. Wrecking ball took it away a few years back