I've said it before and I know many seem happy with their Rega arms, but I found the RB250 and RB300 unimpressive.
I used both, with minor upgrades, on a Technics SL-1210. With my ZYX R100 mounted, both arms worked and produced music, but swapping over to my Mission 774 arm was like somebody had waved a magic wand over the music. The whole thing opened up and came to life!
So put that in yer pipe and smoke it!!