UTG is 15/5 over a sample of 150ish hands. I decide not to 3-bet because I really don't want to play against the top of his UTG range. He seems taggy post flop but no real reads. SB is 40/20ish and BB is 27/18 (same villain from the other hand I posted). Both of their ranges are SUPER wide here if that matters.

Stacks:
UTG ($1916.19)
Hero ($1193.25)
CO ($995.00)
BTN ($1107.50)
SB ($2116.89)
BB ($902.00)

Pre-flop: ($15, 6 players) Hero is UTG 1 [Qh]
UTG raises to $35, Hero calls $35, 2 folds, SB calls $30, BB calls $25

Flop: [9d][3h] ($140, 4 players)
SB checks, BB checks, UTG bets $100, Hero calls $100, SB folds, BB folds

I would raise this flop almost always if I was against a normal TAG but this nit betting into a 4-way pot screams strength to me. Folding even seems like an option here, but that just felt to weak-tight (especially since my sample is not big).

Turn: ($340, 2 players)
UTG checks, Hero bets $245, UTG calls $245

I figure I need to bet to get value from AK/AQ with a diamond or JJ. If he raises I am done. I think I could bet a touch more here...

River: ($830, 2 players)
UTG checks, Hero checks

I don't know if he's tricky enough to check a big diamond here so I decide to check it down. I don't beat much (probably just JJ no diamond unless he made some weird looser than normal preflop play with AT or something) so I guess I could turn my hand into a bluff here...but I didn't.

Thoughts on all streets?

I'd just check back the turn I think. You say you get value from AK/AQ with a diamond or JJ, I say you open yourself up to getting check-shoved on by them and folding the best hand.

You can't fold preflop, you're getting odds to chase a set.