raising for value vs. facing the field with two

[tyler_cracker]

Hero has A3[img]/images/graemlins/club.gif[/img] in MP3. Table is very loose passive except for the TAG to my right. People limp, TAG folds, Hero calls, people limp and complete and check.

Flop (6 SB): A[img]/images/graemlins/heart.gif[/img] 9[img]/images/graemlins/club.gif[/img] 6[img]/images/graemlins/club.gif[/img] (6 players)

checks to MP1, MP1 BETS, Hero...?

Do i smooth call here to invite more customers? Do i raise with my big draw, let some of the fish cold-call (as they surely will), maybe fold a better ace (unlikely, i know), maybe get a free card?

What are the things that push this towards a call or towards a raise?