Having tried Firefox and Opera extensively, I settled on Chrome for Android (Galaxy Tab Pro and Galaxy S5 devices here) since it runs the smoothest for me. On my tablet, I found Firefox to be very prone to crashing for some reason...Opera was quite good and Chrome is very smooth. I didn't spend much time with other browsers since I wanted the ability to sync my tablet, phone and desktop bookmarks, tabs and history.
For ad blocking, I was recommend AdGuard
some time ago and really like it. Unfortunately it's not free; I was lucky and hit a good deal ($7 for two devices for the year) so I'm going to try it for now. It does a pretty decent job and it will block ads system-wide instead of just in the browser. Also note, you won't find it in the Play Store (for obvious reasons) so you'll have to buy it directly from them.
Good luck with your search.