I have the Vr3 and really like it. I had wanted the Vr6 the most because I absolutely love my LELO Ina (and the Vr6 is quite similar to the Ina). But it was sold out at the time I placed my order, so I settled on the Vr3. I plan on eventually adding the Vr6 to my collection as well.
I believe the Vr3 probably provides less clitoral pressure than the Vr6, but since I don't have the Vr6, I cannot say for sure.
I do not believe the Vr4 would provide ENOUGH clitoral stimulation though. I've examined this toy at a local brick-and-mortar store and the clitoral stimulator is so extremely thin and flexible that it does not provide any pressure at all. I think it would just be frustrating.