If you look there are lots of threads on here about this. The answer is that it really depends where your research is and what you are looking for. For instance, I find that Ancestry has a lot of London records including some marriage certificates, but FindMyPast has other records I need.
It is probably best to look for the free weekend offers or cheap month offers and try both to see which suits you. Or see if your library offers access and try them out.
I don't think it is a question of which is best as they both have pros and cons.
