I would vote Lat64 because it's hugely popular now, they have great discs, they have new light discs for kids/ladies, and you could pick up a couple of their bag designs if you want. The only problem from a retail standpoint is that since they have so many beautiful discs, buyers can get pretty choosy and may look elsewhere if you don't have the particular swirl or color on the shelf (not that different from other companies, but noticeable with Lat64).
MVP wouldn't be a bad idea, but whether it gives you lasting sales will depend on your customers. Around here only one place picked them up...they've done a half dozen reorders, but there are hardly any MVP discs seen on the course and there are plenty for sale and trade. Since they're damn near indestructible, you won't see too many repeat customers unless they lose them or want to start a collection. So Maybe an initial order or two to see if they take off? They definitely get attention and next to standard discs they look really nice.
I'm becoming a big fan of Lat64 and Westside and they're sure to sell, but you could possibly reach more people with two smaller orders from MVP and Gateway.
Best thing might be to poll your local throwers and see what they'd like to have.