Wireless Router versus Cable Modem with WAP

I need to replace old Motorola Docsis 2 surfboard modem with a Docsis 3 model. It is currently plugged into a Netgear 802.11n AP.  Should i replace the modem with a wireless router or just replace the modem and keep my netgear?  The 2 approved wireless routers (Cisco and Netgear) DO NOT have external antennae so i am concerned about coverage.