While you are very,very fortunate to have "multiple sitters" (wow, where do I find that setup for my older child?....), your child needs one principal sitter for now whenever you go out. She is too young yet for rotating sitters and isn't able, at two, to get really comfortable with sitters she sees infrequently. She needs consistency and routine, and even if she acts as if she "knows" who you mean when you say "Miss X is coming tonight" or "Auntie Y is sitting you tonight," that does not truly mean she pictures them clearly or has any ability to anticipate that particular person's time with her. I would limit it to one sitter for the next year or so -- even if it means you get to go out less often. I'd do just one regular sitter, and possibly even have that person come over and play with her when you are there the whole time. And then in a year, add one more sitter to the mix, not a bunch of them.
Do always say goodbye. Re-read Megan's excellent post (she's the one studying early childhood). The way to build trust that you will indeed return is to make your departures clear and uneqivocal: You do leave, at times, but you will come back. She needs to know it's OK and that your leaving equals your returning later. If you sneak out, your daughter knows you're there one moment, is distracted by a sitter, then turns around and--you have vanished. She is at an age where she may still believe that when you are not physically present with her, you're Gone For Good. She's on the cusp of getting past that, and the fact she is OK after you leave is very positive, but simply disappearing without acknowledging that you are leaving could make her much less secure each time you leave. Her fusses and freak-outs will actually be worsened over time if you sneak away each time, because she will be uncertain what is happenining and whether you will return.