As someone who's been through it, I agree. Appt. first, then a couple drop in's.
Here are your drop in excuses: Extra questions, happen to be passing by.
Also, they always have paper work for you and immunization forms, so you're dropping them off, wanting to make sure everything is in place for your "crazy" morning their first day there.
The place we go to has become like family, the kids are all friends and many of the workers are moms of kids my kids know. It's a local place put on by a great local lady. Most great daycares will not even be phased by how many times you drop in. They want to answer all your questions and doubts.
If you feel uncomfortable (not in the "l'm nervous to leave my child anywhere"), keep looking. Also, if you go there and feel it is not for you, keep looking. The place we are at now we did not "see" when my kids were first small (even though it was there in town the whole time). I've also found that what my children needed as babies and toddlers is different now as school agers. Some places may be better geared to one or the other.
Bottom line: The staff can change over, but some more than others and the staff makes or breaks it. Watch who they hire because it shows how caring they expect the individuals to be. Appearances are also not always everything.