In terms of behavior or in terms of species? I have various answers.
For soft vore and pouching, I prefer a gentle predator offering innards as a safe place for willing (if possibly reluctant/reflexively recoiling) prey. Endosoma.
For anal vore or messy full tours, there needs to be reluctance on the part of the prey (butts are stinky and gross!) and playful aggression to make it happen anyway, or prey who willingly entered the mouth resigned to the only proper exit being stinky and uncomfortable.
For hard vore and digestive soft vore, I need incitement to JUSTIFIED violence - not necessarily a credible threat to the predator, but maybe retaliation for an (ineffectual) attempt on his life, or more likely a credible threat to an innocent or dependent of the predator. Good pred, evil prey.
For CV and UB, the most important thing to me is that the predator be male and the prey female in the former and vice-versa for the latter. I want them explicitly married to each other, too. To me this is the DEEPEST form of conjugal intimacy, like regular sex run through multiple distillments.
For species, mice are my favorite prey in all scenarios. I prefer a roughly mouse-sized micro and credibly-larger prey to avoid too much suspension of disbelief for the stretching, or human-sized prey with a macro.
Mouse preds are a nice treat now and again; role reversal is a theme I jam to.
Comments
For soft vore and pouching, I prefer a gentle predator offering innards as a safe place for willing (if possibly reluctant/reflexively recoiling) prey. Endosoma.
Mouse preds are a nice treat now and again; role reversal is a theme I jam to.
Least Weasels, Stoats, and other slick, slender living noodles make for very slurpable prey as well.