It depends on what you want to do with the RV.
Class B camper vans are usually 2wd, with low ground clearance. If you like to go off road, a 4wd pickup with a camper in the bed is a better choice. Sure, there are some 4wd vans out there. They are rare and very expensive, compared to the myriad of 4wd pickups available.
A pickup and camper is a multi-use vehicle. Drop off the camper and you can use your pickup for all sorts of things that you can't do with a camper conversion van. This is important particularly if your pickup is your only vehicle.
If you are looking for a dedicated RV-only vehicle, for mostly on-road use, the class B camper conversion van may be your better choice, or a small class C van-based motorhome.
01 International 4800 4x4 CrewCab DT466E Allison MD3060
69Bronco 86Samurai 85ATC250R 89CR500
98Ranger 96Tacoma
20'
BigTex flatbed
8' truck camper, 14' Aristocrat TT
73 Kona 17' ski boat & Mercury 1150TB
92F350 CrewCab 4x4 351/C6 285 BFG AT 4.56 &
LockRite rear