Hero is otb with AA with about 400 in front of him table is fairly tight HJ goes all in for about 30 CO calls CO has about 300 in front of him ( Most of the table had folded before the HJ just one limper) The question is to get more value should hero just flat call or raise to try to isolate the CO and get it headsup with him.

Build the side pot.
Raise to 75-80

Absolutely RAISE !! There's a good chance the co will think your trying isolate and there's also a good chance he has a big hand that he can't fold.

+1

You have to raise make it like 75-90. The caller has a good hand maybe 99-KK possibly AK so it's going to be tonight for him to fold

+1

You are going to have provide for more information on the villain's tendencies before we can provide you with honest evaluation.

FYI, I don't think it is necessarily an automatic raise. There are some villains that I would flat against.

Given typical 1/2 blinds I really don't want this going 5 ways to the flop

Raise to $110 and shove any flop if he flats. Your raise will look like a squeeze to iso the short stack.

Well I did that.....and he shoved for 300 and I snap called HJ had JJ, CO had KK and my bullets I hit a boat on the flop and stacked him. But thinking about it should I have let in one more player ? He later claimed he had A10 and I could have stacked him too since the flop did come down A 10 10.

I seriously can not think of one reason why we would ever flat this flop. We don't want it to go 4 ways lol.
Like if he was shallower and we could get it in otf that would be about the only time I'd flat.

It would have been good on that specific board, but the flop is more likely to come out TT7 and then your probably getting busted. A villain calling that sort of bet behind multiple callers probably has something better for busting big pairs then ATs and is going to know they have to flop a monster to stick around vs the likely multiple high pairs here.

Also note, that if you do flat, the KK hand can get away from it on the flop when the ace hits and there is action. You probably only get to stack one no matter which way you do it. And your only going to stack the guy with garbage if he does catch a good flop where you are still best, while the guy with KK is almost always going to stack off if you raise preflop.

Given the exact villain cards and that exact flop, flatting would have been marginally higher EV but in the vast majority of situations, raising is higher EV.