If I were you I'd look for a P3/24 over the P3. The RB301 arm has a lot of improvements over the RB300, better wiring (same as RB700), better anti-skate system from RB700.
These are the carts you commonly see suggested for the P3/24, depending on budget, they are all good choices:
Rega Elys2 or Exact2
Dynavector 10x5 or DV20xH (or L)
Ortofon 2m Series (I use the Black myself)
Clearaudio MM line
AT105MLX (but some say it is "bright")
You really aren't going to go wrong with any of these. Probably the most suggested cart with Rega is the DV20X line or the DV 10x5.
These are the carts you commonly see suggested for the P3/24, depending on budget, they are all good choices:
Rega Elys2 or Exact2
Dynavector 10x5 or DV20xH (or L)
Ortofon 2m Series (I use the Black myself)
Clearaudio MM line
AT105MLX (but some say it is "bright")
You really aren't going to go wrong with any of these. Probably the most suggested cart with Rega is the DV20X line or the DV 10x5.