Help Settle an Argument

[Huskiez]

A friend of mine played this hand on Stars and told me about it. We strongly disagreed on his flop action. We debated for a half hour, and we'd like to hear what you guys would do in this situation.

PokerStars No-Limit Hold'em, $2 BB (9 handed) converter

MP1 ($179.80)
MP2 ($194.55)
MP3 ($236.85)
Hero ($196.80)
Button ($206.95)
SB ($330.05)
BB ($100.85)
UTG ($52.90)
UTG+1 ($182.20)

Only read is that SB is somewhat weak-tight.

Preflop: Hero is CO with 2[img]/images/graemlins/spade.gif[/img], 2[img]/images/graemlins/club.gif[/img].
UTG calls $2, UTG+1 folds, <font color="#CC3333">MP1 raises to $4</font>, MP2 calls $4, MP3 folds, Hero calls $4, Button folds, SB calls $3, BB calls $2, UTG calls $2.

Flop: ($24) K[img]/images/graemlins/spade.gif[/img], 2[img]/images/graemlins/heart.gif[/img], Q[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(6 players)</font>
SB checks, BB checks, <font color="#CC3333">UTG bets $10</font>, <font color="#CC3333">MP1 raises to $20</font>, MP2 folds, Hero ...

Should hero call or raise (and how much)? Why?

Why is calling superior to raising, or vice versa?