Take your pick, pretty much any of them are fine for hobbying.
This thread contains the info you are looking for regarding security/elevator etiquette.
http://eccie.net/showthread.php?t=716124
Also, keep in mind at elevator security procedure can and do change from night to night at most places. Some days/nights there will be and others there won't be anyone there.
Things work a bit different than you are probably used to in most other areas.