There's really no magic number to aim for I don't think. A general rule of thumb is try and keep the VPIP and PFR% as close together as possible and keep your aggression above 2. You can be a solid winning player with a 25 VPIP or a 15 VPIP, it's really dependent on your favoured style.

Personally I'm happy if I run 20/17/4 but anything around that is ok.

EDIT: That advice is for 6max NLHE

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