Staying in the city would be nearly as convenient. You could check in for tickets and baggage check at either the Central/IFC station or at the Kowloon station. There are free shuttles from major hotels to the airport express station from all over the island. I believe the checkin cutoff is 90 minutes before your flight. Then you hop the airport express to the airport (<30 minutes), head through security and to your gate.

Means less time wasted at the airport from check-in to departure and gives you more hotel and nightlife options being on the island.