5er and the tow truck has 2 in 1 snug fit, very stable and easy to drive ; while TT and the truck are always 2 units, unstable. easy to get fish- tailing when driving , especially in high winds.
Suggestion #3 : Try to get a SUPER DUTY PLUS truck with diesel engine. ( eg. Ford 350 at least, F450 is better ) that will give you enough power not only to pull trailer up mountains, but most importantly to SLOW DOWN trailer down hills. This is a safety issue. A super heavy duty truck with diesel engine can last 25 - 30 years and handle trailers of feather light all the way to those over 45' long, 20,000+ lbs. So no matter how often you change your trailers, you don't have to change your reliable truck.
Suggestion #1 : find some good RV books to read before you buy anything.
PS: We are full time RVers of over 2 years with a Ford F350 dually diesel truck and 40' long 5th wheel trailer with 1.5 bath and washer/ dryer. We chose these combination because we didn't want to deal with 2 engines ( classA /classC + toad . And it's not an option without a toad car ) After 2 years living on the road, we only find a few small things not meet our ideal demands. If some day we have to change our trailer, we would like to have a same size 3 -axle 5th wheel toy hauler, which is more versatile , can offer lot of storage space for your toys and many beds at the same time.