If you have a good pc, i shoud go with fslabs, if u have a low pc, aerosoft is better, fslabs simulates better the real world, like ice, anti-ice, system failures etc...
I think is clear by now that one is no better than the other but all depends on what you are intending to use it for. FSLabs is one of the most advance simulation to date together with PMDG so you really need to be prepared to learn or know al ready to enjoy it (and of course it come to a cost of a bit of extra demand on PC resources).
Aerosoft is more a enjoy thing, very very eye candy at little fps cost and more simplified flying needs. Still great in my opinion and providing plenty for a high percentage of simmers, but never was aiming to replicate the real plane.
In common,they are both very good for what they are intended.