I'd get an V4.
To me it feels like Bandai took away too many of the good features on the V4 (the school/jobs, the mail, age/weight display, connectivity to previous versions) and added too few new features, and poorly executed:
-On the V5 you raise 3 characters at once and have them on screen at the same time. BUT you can't select which one you want to feed, clean or play games with.
-The screen has more resolution and the contrast can now be adjusted. BUT even adjusting the contrast, the screen is a lot harder to see.
-You get to name the family at first. BUT you can't name each individual character nor name the children in later generations.
-The pause feature is still there. BUT it's now hidden and activating it is too time-consuming.
-There is a new stat to raise, the "Bonds percentage". BUT there are no skill points.
IMHO the V5 strays too much from traditional Tamagotchis. Bandai shouldn't have called it "V5", instead they should have left it at "Familitchi" or "FamiTama" (like the TamaSuku).