Personally I like P7 for the morphing tool, the multi-level undo, and the faster rendering (and the fact that it will render things that P6 couldn't handle on my computer). The main bugs with P7 that cause me problems relate to the cloth room - recalculating dynamics when you have more than one item of clothing on a figure makes it go haywire, but can be worked round by deleting the simulation and starting again.

On the female figures, over all I personally prefer V3 to V4, mostly because of the range of stuff available for her, and  her more mature looks. V4 always looks more like a teenager to me, though she does morph well.  V4 is also a resource hog; poser noticeably slows down when I load her, and I suspect that she makes P7 less stable. I certainly get more bits of poser weirdness when I have her in a scene than when I use other figures!  Having said that, I suspect V4 is the future and there are some very nice items being produced for her.

One more concrete suggestion; when you decide what you do want,do consider a Daz platinum club membership and/or a Poser World subscription. Depending on how much you expect to buy both can be very cost effective.

"Don't make me angry. You wouldn't like me when I'm angry!"