You will make more money if you raise. T9o is 43% against 2 random hands, but 51% against one - you want to play this one heads-up for the most +EV.
Calculations assume $1 BB, SB calls whenever you limp, SB folds whenever you raise, no raises pre-flop, and 100 hands run.
Against 2 other random hands, T9o is 43%.
You should win 43 x $2.00 (BB + SB) and lose 57 x $1.00
43*2 - 57*1 = +29.00
Against 1 other random hand, T9o is 51%
You should win 51 x $2.50 (BB + SB + BB_call) and lose 49 x $2.00
51*2.50 - 49*2 = +29.50
Looks almost even at first glance, but if you raise, sometimes they will both fold. The possibility of winning the hand without a showdown (either pre-flop, or with a continuation bet) makes the raise more profitable than a limp.