The Trailblazer would be easier to tow, but you will probably be at or over the max weight that is recomended, usually 5000 lbs. And, that is a heavy toad for your rig.
We have a 28 ft Lexington, same E-450, and tow a 3200 lb Subaru without any problem. Lexi is rated to tow 5000 lbs, but no way would I tow that weight unless absoultely necessary.
Some newer class c E-450 are rated to tow more now, but thats pushing the limit of whats safe, and what the rig is actually capable of towing over a long distance.
Prius will require a dolly, but will keep your towing weight within reason. Dolly would probably be a bit cheaper as you won't have to buy any 4 down towing equipment, usually 3 to 4 grand, total for all the equipment and supplemental brake system.
Only problem you may have is storing the dolly when not in use, either at the campground or at home, depending on your residence.. Most campgrounds you'll be able to detach and store the dolly right behind the rig, but some may require you to put it in an "overflow parking" area.
Steve & Cheryl + Charlie & Casey, our furry kids.
2012 Forrest River Lexington 283ts
Toad, 2013 Subaru XV Crosstrek
Camping trips this year so far...8