How do you bet bet smaller pairs on the Flop?

[Offsuit27]

small or middle pair, or a pair from your hand?
lets say there's someone behind you that you can assume has at least one over card, small bets preflop, relatively small pot compared to stack sizes. say 150 in pot and 1500 in the stacks.
mathematically, what's the right bet?
what if there are 2 opponents?