A healthy, varied menu. Kids will try things at nursery that they won't try at home, a healthy menu at nursery takes the pressure off at home.
Good staff retention, continuity of staff as they progress in careers, move between rooms.
Extremely enthusiastic staff and genuinely so!
The facilities are somewhat secondary to me, other than that the toys and so on seem clean and new, replaced regularly. DD used to go to a nursery with spectacular grounds and buildings. Her current nursery is much smaller but the staff are committed and enthusiastic and THAT to me is the difference!
Not fussed about trips, I can do that myself. Special visits from people like the Fire Service are good though.
Less important to me than getting kids academically ready for nursery is help with being independent - hygiene, teeth brushing, going to the toilet, washing hands well, coat buttons, zips, shoes, etc. Programmes to tackle these things are good.