Collector's is for collectors. You need to be prepared to drop a lot of coin on a purchase, but you will get a very nice product from them. I picked up 2 38/44's and a couple of 210's and a few Dan Wesson's from them. Very nice to deal with, but expensive.
Fountain is just plain friendly helpful folks. I particularly like to work with Oren and Sloan. They did my other 210-5, the custom Baer's, several 5 screw S&W's a few springfields and CZ's and finally my Dan Wesson Razorback. Good prices, great service nice folks, small selection (compared to Collectors).
Either will treat you well.