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.
Both of them are not in the same league. Primedice is pure dice games but betcoin.tm is casino that have many games on it. And if I can say for casino games betcoin.tm is a great site. From the total online players and the huge jackpot around 95 btc. I do think that he is owning other casino in his league