Hi Boatshed, yes live in Canada but Yorkshire born and cheap!
Have used both of them.
My experience is that AliExpress seems to have a larger assortment of fasteners etc. although they do offer a wide range of products.
Banggood seems more focused on specialist equipment for our hobby.
Aliexpress is cheaper. Think as many of the products are similar, it is due to their shipping methods. Cainao, which does most of their shipping is poor. Cheap with poor tracking, they have no idea where anything is. Eventually it will turn up unexpected and unannounced.
Bangood shipping can be tracked and is usually quicker.
In fairness to both, have received all my orders eventually.
Am very happy with Bangood brushless ESCs. Much better modulation than Turnigy, with no programming (suites me as am not seeking pure performance, just reliability) and less expensive.
If you can plan ahead and place orders before you need an item, either works. There are significant cost savings when compared to the more traditional suppliers.