I am just curious what stats do other use.. also how big of a sample size do we need to for these to take effect?

I use the hud provided by the PS elephant...

VPIP Avg / SB OpenRaise / BB Reacting to SB OpenRaise / PFR

AFq / W$@S / WTS / Hands

Cbet Flop/ Fold to Flop Cbet / Cbet Turn / Fold to Turn Cbet

the only I am not sure about is BB Reacting to SB Open Raise...what does this value mean.

The only stats I actually looked at today was WTS/W$@s & flop/turn cbets & fold to cbets

What other stats are useful over small sample sizes I don't have a History with many players.