Location, location, location. Not meaning it has to be popular, but meaning it should be a good port: protected from the elements, a reasonable approach and reasonable proximity to places I want to go.
Next, it has to be in reasonable repair
. I don't want wobbly docks that one nearly falls in the water while transiting or lack proper protection or power/water fails continuously.
Shore toilet/shower facilities (guests really like a break from showering aboard, sometimes I do too)
Desirables, but not deal killers:
Onsite service staff (but they need to be good or are just an impediment to getting the right talent)
Basic parts supplies available (oil, filters, clevis pins)
Mix of power and sail, which seems to allow for better overall comradery when there is a balance of power.
Pool, restaurant. Nice to have, but don't care.
No control whatsoever:
Price. Around here, you generally get on a waiting list to get even some of the above requirements, so you pay the going rate or you don't. I know of a couple of untouchable marinas that price strictly for the uber-rich transients, but I woudn't want to be there permanently anyway.