100/200, Huge pot. Value bet the river?

[4thstreetpete]

Party Poker
Limit Holdem Ring game
Limit: $100/$200
9 players
Converter

Pre-flop: (9 players) Hero is Button with
<font color="#cc0000">UTG raises</font>, 2 folds, MP2 calls, 2 folds, <font color="#cc0000">Hero 3-bets</font>, 2 folds, <font color="#cc0000">UTG caps</font>, MP2 calls, Hero calls.

Flop: (19.5SB, 3 players)
<font color="#cc0000">UTG bets</font>, <font color="#cc0000">MP2 raises</font>, Hero calls, UTG calls.

Turn: (12.75BB, 3 players)
<font color="#cc0000">UTG bets</font>, MP2 calls, <font color="#cc0000">Hero raises</font>, <font color="#cc0000">UTG 3-bets</font>, MP2 calls, <font color="#cc0000">Hero caps</font>, UTG calls, MP2 calls.

River: (30.75BB, 3 players)
UTG checks, MP2 checks, Hero ? .


I've been thinking about this hand all day.

UTG and MP2 villains are your standard 18/10 weak tighties. Very good table though and I've been doing well and having my way lagging it up.

Can UTG have anything other than AK (with a flush draw on turn) or a set here? What about MP2? raising the flop and calling all the way. He's got to be on a draw because I think 2 pairs is out, possibly a set.

The river is really bad because both the straight and flush gets there. I'm confused here because they both checked (?).
Is this a very easy value bet based on the size of the pot?