We took a long time to decide on an RV. It was our first try at this. I went to a couple dealerships and to the RV show at Hershey. This let me look at the different floor plans. I knew I wanted used but the floor plans don't change that much year to year, going to the Hershey RV show let me look at several in in detail the same afternoon.
Once you find an RV have it checked out by a third party who works for you not the seller. The older the RV the more important that check is. Older RV can have a lot of hidden damage that will cost a lot to repair. This is just like getting a home inspection before buying a house. Also have a mechanic check the truck part, the same as you would do with any used car.
When you decide to buy have the owner go through all the systems with you. Operate the stove, generator, toilet, water pump, sinks. Have him show how to dump the waist tanks, where the hoses are located. He should show the manuals and any related documents. Sometimes the manuals will not be with the RV in that case be sure to take good notes or use a video camera to tape the instructions so you have something to refer to the first few times you use the RV.
Good hunting. Keep the search fun. If it starts to become work take a break.