I have played on PrimeDice and BetKing. Both of them are great actually with better user interface and fast payouts. Dice games are best in PrimeDice right now and it is one of the top Dice gaming websites. 
I would say Primedice is the best to play Dice.
I think they will if the roll speed increase. Now it's kinda slow.
Based on my experience, in automated betting, it is faster now compared to the previous version. Disabling the animation makes the rolls faster.