At the end of the day, the story's going to end the same way, so it really doesn't matter which scenario you play first. I think it'll make sense in any order, but I'm just going to play it the way Nomura said to play it.
The world stories have an order to them though, if that is important to you. but for the most part as long as you go Ven --> Aqua it'll be ok. Terra can fit in either the front or the back.....
Some one's going to quote that out of context I know it....
Beginning or end.