I think is primedice and betcoin.tm. I guess.
Primedice have a great giveaway.
Betcoin.tm have big promo and a lot bonus
And both this site have a alot of member.
I highly doubt that betcoin.tm can be measured or compared with primedice since they were to the most people totally unknown few weeks before.
Now they started a ton of promotion, but that still doesnt put them to the richest spot, that only means they want to expand.