for opponents i use a system for betting and calling behavior

For betting behavior i have 3 to -3, 3 being very aggressive, -3 being very passive, 0 being an even mix.

Calling behavior is pretty much the same, 3 being very loose in what they will call with and -3 meaning they will fold everything but the nuts.

i also like to remember how they play draws, whether they slow play, etc.

For myself, i play live games, but if i were you i would right down the hand #s of key hands and use poker tracker to analyze later.