Great question with lots of answers. I think it comes down to how well a floorplan and the planned use for the RV fit your lifestyle. Take a look at both and compare. This is very much a personal decision and one based on your needs and abilities along with a good dose of what you really want. I do think it's a bit of a preference thing. Some people are motorhome people and some are trailer people - either way you're still in an Airstream
I've not owned a trailer so all I can do is tell you about our experiences with the motorhome and why we ended up with it.
We have three kids and opted for the motorhome to make about three long trips per year (1000+ miles each way). It is absolutely the most comfortable way to travel with all of the convienances of home available while traveling at 60 mph. I'm a "driver" so when I get behind the wheel I turn into my father and want to make good time. The motorhome helps me in this regard as with an 80 gallon tank and a rolling bathroom, kitchen, dinette, LCD screen, DVD player and Playstation onboard. we don't need to stop very often.
In addition to these long trips, we also use it for local camping about once or twice a month; mostly overnight trips and it works fine for that as well. Pull in, un-hitch the TOAD, back into the spot, flip on the levelers and roll out the awning - within 10 minutes - we're camping! I also really enjoy explaining to other campers that "it's an Airstream" and "Yes, they did make motorhomes for a while".
We thought pretty hard about a TT but decided to try out Class C rental for a week just to see what it would be like. (I highly recommend trying a motorhome this way.) It only took about 250 miles for my wife to decide a motorhome was for us. Being able to getup and make PB&Js or help with a potty break or the million other things she does while we're on a long trip without stopping made a huge difference for everyone on board. And overnights enroute mean you don't even need to get out of the MoHo.
We recently added a lightweight TOAD to pull behind the motorhome. It has made it an even better platform for our needs. I give us the flexibility to travel easily from the "mother ship" wherever we end up. I've been known to find a Starbucks and head out to bring some "home".
As far as maintenance and breaking down. Honestly, we've had our fair share of it. Most of the Classic are 20+ years old and need care and attention. Ours was what could only be called a basket case when we bought it. It took a while to make it reliable and for me to learn about all of the systems, but we got it for a song and even with the investments we've made in repairs and upgrades, we're in a good place with it. (Think boat ownership). The TOAD concept also comes in handy on these occasions when the Airstream needs a part (or just a rest). We now refer to our TOAD as the LEM (Lunar Escape Module) so my wife and the kids can go sightseeing while Dad fixes the Airstream.
Even with their age, they are on very common, inexpensive platforms (Chevy P30) which as someone already pointed out have cheap parts and lot's of mechanics qualified to work on them. If you're even remotely handy you can fix most items yourself with the right information and some patience. If you need a mechanic to check your oil then a Classic Motorhome may not be a good fit for you.
If you're FT you are going to want as much space and storage as possible. Our 345 is bascially the same as a 34' TT (without the dinette in the nose). I would not say any of the Classic have a lot of storage, but as with most Class A's they were built for full timers. Our 345 for example gives us two distinct "zones" seperated by the bath...the kid are up front and we're in the back (unless we're underway
). Space is good - very good in fact. I would imagine that a trailer would have better interior space utililzation, but the motorhomes do have a few exterior lockers for things that don't belong inside anyway.
Regarding economy - Since you'll need space you'll need a long Airstream. I can't imagine a truck with a 454 pulling a 34' TT with another car behind it will cost less to own/operate than a truck with a 454 and a 34' TT "bolted to it" would.
Lastly, price. You can get some pretty good deals on MoHo's right now as gas prices are what they are. Let's say 20K for a decent 345 out the door. Plan on spending another 5K on repairs, fixes and upgrades in the first year, Less in the second and so on. Insurance on our RV is less than on our 96 Jeep. Every time I think it's too expensive to keep using it I do the math. It's still the cheapest way for us to travel the way we do.
We love our motorhome and can't imagine it any other way. IMHO.