I didn't actually like Casino Royale, it might have something to do with me having a big dislike of poker, and you take that away and it's not the best film. Quantum is one of my favorite Bond films there is though I'll admit most don't agree with me on either point.
I love them both, Daniel Craig is easily my second favorite Bond.
And despite my tendency to be nostalgic, my favorite isn't everyone's favorite curmudgeony Scot.
Edit: I think Quantum sadly fell victim to be the "middle piece" of something that left people wanting more. From a storyteller perspective I felt it was both well made and well written.
It's just not a marvelous stand-alone piece.
Oddly, the Empire Strikes Back tends to be so many people's favorite Star Wars movie, and it's pretty much in the same situation, so...