I personally use Bromite: https://www.bromite.org/

From my (anecdotal) experience, Bromite is faster than Firefox on my phone, but your mileage may vary.

I was originally using Firefox due to its uBlock Origin support, but Bromite has ad-blocking built-in (unfortunately it's not quite up to par with uBO but it works well enough).

I would suggest that you try both and see which one you prefer.