Depends on the purpose.
If I intended to mount a scope I'd get the RB, it is the heaviest/strongest of the three and designed for the hunter. The 6 shot 44 is a nice S&W N frame clone that serves well for open sight hunting/plinking. The tracker is a 5 shot that weighs less making it ideal for an occasional plinking/trail gun (although the porting can be loud). If I didn't have a specific purpose in mind and just wanted a 44, I'd pick up whichever was on sale!