The variety in RVs is like the salad dressing aisle at the supermarket.
Take the time to define what you want to accomplish with the RV. We're very happy with our small travel trailer (18 foot), and oversized (1 ton diesel pickup) tow vehicle.
This meets our wants because
1. It is just enough room for the family of three, and the dog and cat. Previous experience kenneling pets for vacation wasn't so good. When the kid grows up/out the additional space compensates for a more creaky body (hopefully).
2. It is small enough to get most spaces at forest service campgrounds. We have come to love forest service camping. No hookups, but water and pit toilets usually available. And more privacy than most other campgrounds. Our overriding purpose was/is to camp, as in to get away from people and urban sprawl to be with nature.
3. Dropping the trailer at camp gives us flexibility to go explore without concern for height/width/weight restrictions.
4. The big tow vehicle means that we're not restricted to the slow lane. There is always the power to get up the hill, and the engine brake to slow down the other side.
We didn't get a Class A because $$$, and it wouldn't fit in the driveway, and they have a bunch of crap that we don't need (outdoor television, washer/dryer, indoor television, etc.)
We really liked the Winnebago Revel (Class B), but it wasn't set up for three people to be comfortable.
We almost did a truck camper, but we're glad we have the TT because of #3 above. Dropping a trailer is way easier than a truck camper.
We skipped the Class C because of #3 also.
This summer we've done about five trips, with the highlight being three weeks around Glacier NP. Our one stay at an RV Park was disappointing, and so we avoid them like the plague--just too close to your neighbor for our taste. State park camping can be good, but still usually close to your neighbor. The NP campgrounds are crowded, and have small sites. So you need a smaller rig to stay there. They do get you close to the sights though, and for very reasonable $. There are RV resorts that cater to those with a need for lots of amenities, and exclusion of the riff-raff. Next summer we're headed to Denali, AK but we'll take a month to get there, and another month to get back.
Overall, start by looking at floor plans. You're buying a home on wheels, so it has to be livable for you. Then move to quality and amenities. Keep in mind that while there is everything under the sun for sale, most of the ingredients are the same across RV manufacturers (appliances are made by Dometic, Class A,B,&C are built on American truck/van chassis, etc.) So it really is like shopping for salad dressing, just 20,000 times the cost.