Sneak attack ‘em when everyone leaves so you can enjoy digesting them in the comfort of your own home~

Hmmm.
Either 1 or 2.
1 if don't know them personally.
2 if know them personally.

Then enjoying mingling with their unaware friends and acquaintances.

2 and 3, honestly. It's important to give guests a chance to have fun.
Half the fun is enjoying their company, build the tension up a little.

4: when Im hungry. Ill try not to eat someone entering the party immediately, but sometimes the food available just isnt cutting it. Ill usually try and eat the host of the party first though, if thats the issue

I feel like two would be the most fun :D

1 or 2. But 4 if they won't stop one sided flirting

I'd probably find a way to pull them away from the party into privacy before eating them

It really depends on the party. It might be easier to take your answers and instead list when it is appropriate to claim a prey at that particular time.

#1: When the prey is unwanted at the party, either by the participants because of personal reasons, or by friends and family of the prey who didn't want them going. Especially if it is known in advance that the party will not be safe for the prey. And not just in the sense of protecting prey from other predators. Prey who get violent when drunk, for example, are another good example of a party goer who *ahem* should be isolated from the festivities as soon as possible.

#2: If there are other predators present at a vore-themed party, or of your predatory chops have been made known in advance, then "the spur of the moment" is usually the best time. Especially if you know that there is another predator who was going to go after that particular prey. But if you're the only predator, or all preds have been warned against predding, then your best bet is to wait.

#3: If you're an endo-pred, or just want a good excuse to pred, go for the ones who are too drunk to drive. If you have one specific prey in mind, this is when you stalk them for a block or two before nomming. And if you want to maximize your haul, start inside with the stragglers and/or hosts, then round up all the ones who are leaving while sober, and finally come back to clean up the ones who partied too hard off the floor, lawn and/or parking lot.

Those are some pretty good answers :p