Recreational Vehicles (RV) are generally divided into two major classes or RV Types. Motorized and Non-Motorized. This is a pretty good classification because decisions between the two classes have pretty big impacts on price, flexibility, maintenance costs, and overall complexity of the RV.
If you have a pickup or SUV of any type you might lean towards a towable because you wouldn't need to purchase two engines (one in the RV and one in your pickup/SUV).
If you are starting from ground zero, then you might pick between the two classes equally.
One of the BIGGEST decision factors on picking between the RV types is deciding on how you will get around when the RV is parked and you want to drive to a nearby restaurant or fun local attraction. If you don't mind a F350 Dually as your everyday vehicle, a towable is just fine. If you want to tool around in a smart car, you probably should consider a motorized RV.