Really depends on what you need it to do. Paxton's a great system for all general purpose access control but if you wanted lift control, then I would recommend Inner Range or Honeywell.
If you're looking for a system with lots of doors and difficult cable routes then perhaps a Salto system would be good (then you need to decide whether it is offline or online).
So many systems, so little time. It all comes down to your requirements and what info you would like to get out of it. e.g. time & attendance, fire alarm integration, reports & alerts, other systems etc.