DW and I are new to TT's, we went small (18') for various reasons. First it tows well with our Jeep Liberty CRD (though we plan to upgrade to a larger Grand Cherokee CRD soon), Second, being small, it forces us to spend time outside which is why we got the TT in the first place, when we retire (long ways off, we are still in our late 20's and early 30's) we plan to live full time, then we will get the big 40' diesel pusher with slides and 60" TVs ;)
For where we are at in our life a small trailer is perfect for us!!
As others have said, thats why theres so many options out there, RVing is not a one size fits all club :)