This seems to be the "mother" of all debates with the exception of breastfeeding. I, too have been debating it for the exact same reasons for a while and my daughter is 18 months old.
I would suggest taking her part time at first, maybe 2 days a week to get used to the idea. Make sure the center is certified with no violations but also that the employees are certified as well in CPR and First Aid. The more education the employees have in terms of child care training the better! Talk to the employees, find out what their training is and why they want to work in daycare. Talk to other moms that take their kids to the center, do a walk through to check on safety and cleanliness. Observe the children, do they look happy or miserable? Find out their policies on illness and what they serve for food or if you have to bring your own.
NYC has a website that lists daycare centers and home based centers in your area that are certified and if they have any violations.
To answer your worry on illness. It is actually better that your child be exposed so she can build up a resistance in her body. Constant avoidance of germs is more dangerous and can make her more vulnerable to getting really sick from an otherwise non serious virus.
It is great that you want your child to interact with other children and many daycare centers do have a learning cirriculum. Just do your research first. You may have to visit many centers before you decide on the right one for your daughter. Good Luck!