(I go into great detail about my setup on this thread
I have two Xbox 360 Slim models (bought summer 2011, built-in wireless n), a 50 down/10 up connection, and an Apple Time Capsule which is now several years old (potentially 1st gen; maybe 2nd gen).
We have had inconsistencies with NAT on our consoles. We can boot them both up and both will have moderate NAT, boot them up and one is open the other moderate, etc. We can then turn them off, turn them right back on, and have open NAT (or moderate, or a mix between the two consoles — it's NAT roulette).
I thought I had read before that plugging in through Ethernet should resolve any issue with moderate/strict NAT (maybe that's wrong?), but we get moderate NAT even when plugging in through Ethernet. So, WiFi or Ethernet, we get NAT roulette, and a diminished experience when both consoles are on Xbox LIVE at the same time (like, say, when we want to try and play multiplayer on Call of Duty: Black Ops II together).
I feel that my connection ought to be strong enough to support two systems on LIVE at the same time. If you read the other thread I've linked, you'll see I mentioned that I tested plugging an Xbox directly into our modem and had little issue, so I'm thinking that the problem may lie in the router.
So, anyone else with a multiple-Xbox setup that could recommend me a good router? I'd like a wireless router for the other devices in the house (notebooks, smartphones, etc.), but have no problem plugging the consoles into Ethernet for gaming.