Rent first to assure that you will like living in an RV.
Pick the layout you want.
Go to lots of RV shows and dealers and spend time in each type simulating everything you do including bathroom and shower.
As other have said, try and decide which type of camper you are and match the RV to that style.
We moved up from a pop-up to a class C.
Only two of us so we didn't need the cab over bed.
Did not want to tow a car so opted for a short 22 foot RV.
Wanted simplicity so opted for no slide outs.
No slide out makes breaking down camp much easier. We just unplug electric if we have it and drive away.
Originally wanted a class B but opted for a small class C for higher ground clearance, bigger bathroom, larger tanks and overall roomier feeling.
Found the interior that fit our needs.
Fold down Murphy bed that deploys in one minute.
Large comfortable couch and bright roomy interior.
Only fits two people so I can't take any relatives. :-)
Take your time and decide what is best for you and your style of camping.
Two one month vacations and never needed a tow vehicle.