When I was looking to buy a new router from Ubiquiti, I looked at the Unifi Router and the EdgeMax Router. I went with the EdgeMax Pro https://www.ubnt.com/edgemax/edgerouter-pro/
The Unifi Router is a bit more friendly for Home / Small Business users (Point and click user interface). The EdgeMax routers do give you the GUI option but you also have access to cisco like command line interface. I do know that you can upgrade to 8GB of RAM for the EdgeMax Pro.
Data Sheets
https://dl.ubnt.com/datasheets/unifi/UniFi_Security_Gateway_DS.pdf
https://dl.ubnt.com/datasheets/edgemax/EdgeRouter_DS.pdf