IMO NXT is aimed more at the cyptocurrency community, with the new Monetary System designed to allow altcoins to be built on top of NXT quite easily.
Bitshares is aimed more at the world outside of the crypto community with support for the digital dollar and other pegged currencies.
Why make this distinction at all? It's not really a valid one.
If the crypto community has any future, it will be by merging into commerce anyway, so this point is rather moot in the long term.
Also, the MS is nót aimed at creating alt-coins at all. It's aimed at creating tokens that have many other uses beyond being "coins", just as the Asset Exchange is not aimed at creating "shares", but rather at creating easily trading tokens of another kind.
Don't mistake the label for the substance.