It's not a matter of "better".

Everyone has their own figure of preference, and if they don't consider something "broken", why the need to switch?

V3 is my preferred figure because I have a ton of clothing and skin textures for her. I have V4 but TBH aside from goofing around in Poser with her I have never done a render with her in it.

Some say that the joints on V3 aren't that great, but I haven't noticed an issue with that. But then again i have never tried to turn her into a pretzel shape either.

I see that people complain about V4's arm pit area and that there is a script to fix it. So she has her problems too.

There was a thread not long ago similar to what you are asking.  You might want to have a look at it and it might answer some of your questions.

http://www.renderosity.com/mod/forumpro/showthread.php?message_id=3039206

On that note I'm heading to bed. It's only 8pm but I can't keep my eyes open,  LOL

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi