What are you going to use them for? Follow FredP's advice.
I'd go for Model Pack 4 first, one can never have enough characters. Then 3, one can never have enough segments and so on. I wouldn't buy model pack 5 at all, what in the world do I need more guns for? That's my opinion, but will it help you?
I don't understand questions like these. These packs are so differenty in what they offer, there is no better overall buy at all.
You need to determine what kind of game you're going to make and then buy accordingly.
Aan jou de beslissing
(Dutch for the decision is yours)