Help me pick a VoIP/Analog/FXO Gateway

I would like to pick up a 4 line or larger up to 8 line external VoIP/Analog/FXO Gateway.

Was looking at a Grandstream GXW4104 IP Analog Gateway


Grandstream GXW4108 IP Analog Gateway


Cisco SPA8800 IP Telephony Gateway with 4 FXS and 4 FXO Ports

What would be a easy one to manage with FPBX that works well. Any other suggestions/models I should be looking at?

We run 2 PBX servers (one for backup) so going with an external gateway seems like a logical choice.

Any thoughts one what to use, feel free to suggest a different model as well.