Both Opera Mini and UC browser are trying hard to take the lead but Opera Mini is still a winner.
I know most of you do not believe me but GOOGLE search trends shows that Opera Mini is the winner. Go to GOOGLE search trends and see the result. You will agree with me.


UC browser is no match of Opera Mini. You see the peak of UC browser is very small. Search results of all countries shows that Opera Mini is the real winner.
The results also shows that Opera Mini and UC browser are not so popular in Russia and some other countries.
I personally use UC browser and and it is a great browser but unfortunately Opera mini is the undisputed winner.
Result:
Winner: Opera Mini