The Blue Circle 21 is good (although I have only auditioned it in an all BC setup and not mine), as are the Classe preamps, as far as warmth and musicality are concerned. Did you want tube or ss? However, my favorites are still the McIntoshes. They have the most impressive soundstage, sweetness, and clarity (awesome noise specs). I just love my little C712 - it is addicting. I temporarily swapped it out with the classe c35 and still like the 712 better (although to be fair, the c35 is cheaper). I like simple preamps. Besides, I love the Mc glass and knobs rather than pitiful little buttons so many pres have. The classe remote is much nicer than the Mcs but the sound is what I am most interested in. The XLR connections make a noteable difference but it is tough to compare directly with RCA since the cables are inherently different. I can't for the life of me figure out why CJ won't offer xlr. Oh well... Anyway, you cannot go wrong with any of these IMO and which to get will ultimately be personal taste. (with the C712, I use McIntosh mc7100, Sony ES, Paradigm Reference 100.2, all MIT cables).
