Whether a motorized unit (motor home) or a trailer is right for you another big decision relates to the size you need and/or want. The best way to begin making this decision is to hit the RV Dealers on weekends or whenever you can. If you live in a large metropolitan area you should have a great deal to see. Finding a large RV Show is also a plus. It is worth your time and effort even if you have to travel to one, but make certain there will be plenty for you to see and evaluate.
Comparing a Class A (usually the largest) and a Class B (usually the smallest) and a Class C (you will note the overhang over the cab) is a lot like the old saying about apples and oranges. One thing you will quickly learn is that, like life, there are trade offs. If you want all the comforts of home be prepared to get 8 miles per gallon or less. If you are willing to make do in a smaller unit (they have most of the same amenities only in much less space) then you can improve your gas mileage to as high as 18 to 20 mpg. Before you decide, spend some time in one. By that I mean sit and walk around and think about how you would cook, use the shower, or watch TV. Where would you store dishes and clothes or whatever you would be taking along.
If possible drive a variety of sizes and determine how comfortable you are with each. No matter how nice that 40 footer is, if you don't want to drive it, you won't. Buying an RV is an expense, but buying one you do not use is simply a waste of money.