let me say up front that I am a retired state employee who now works in camper sales .... we camp extensively, just returned from a 71 day cross country swing ... there is no perfect style camper, they all have advantages and disadvantages ... many of the comments already listed are dead on and some may be off a little ... we have towed our current TT for just under 40,000 miles during the last 3 summers and currently are having a 5er custom built that should be here around the middle of October ... from our experience, advantages and disadvantages are as follows:
TT:
1. several modern hitches deliver extremely smooth towing with minimal (if any) sway so the tow-ability differences that used to exist are now almost nonexistant ... the pivot point difference is one that is up to personal preference
2. may be towed by a variety of vehicles (vans, pickups, Surburbans, etc)
3. have fewer steps (the older I get the more I like this feature

: )
4. free up the bed of a pickup to haul other items
5. across the board have more floor plans
6. are generally cheaper
7. lower profile makes it easier to travel through parks with low hanging limbs
8. lower profile also reduces the impact of head and cross winds
5'ers:
1. more living space than a TT of the same length ... most, certainly not all, TT's count the tongue as part of the lenth of the camper
2. shorter length going down the road ... a 30' TT is all behind the tow vehicle while a 30' 5'er extends over the bed of the tow vehicle
3. in most (certainly not all, with the exception being centered mostly in the midwest) states, if a person wished to pull two trailers (ex: camper and a boat) the first must be a 5'er
4. can usually accomodate some options that most TT's can't (example: a generator)
5. most have considerably more storage space than TT's
6. many are available with more advanced suspension systems (like the Mor-Ryde system) that are seldom found on a TT
7. where height is not an issue, a 5'er and its tow vehicle can often be parked on a smaller site than a TT and its tow vehicle
the bottom line is which do you like the best and will provide you with the best service ... when looking for a used camper its age/condition, floor plan, the tow vehicle, manufactor (quality of construction) and quality of dealership are critical factors ... buying from an individual is fine but all of the above factors should still be considered
if you haven't done so already, check out the following general RV forums:
http://www.rv.net/forum/
http://irv2.infopop.cc/6/ubb.x?a=cfrm&s=8076099152
the best brand specific forum I know of is:
http://www.sunnybrooktalk.com/members/index.php?
hope this helps
Jim