Ditto what others have said, go with ethernet whenever possible and 100Mbps is more than enough for ATV.
For those with an interest in the bits and bytes of why preserving capacity for WiFi only devices is a good strategy, a look under the hood of the tech is helpful.
There are two aspects to the strategy. One is bandwidth, think of a highway at rush hour. A one lane road can handle X cars, two lanes, X * 2, etc. Networks have limits to how much traffic can pass through a port, and WiFi is basically a single port on the network. Yes, some WiFi routers have multiple frequencies, but everything passes through a single port to the wired uplink or even between the radio receiver\transmitter and network ports.
Routers and Access Points have bandwidth limitations on both a per port basis, and on a device basis. Part of how the bandwidth is accommodated is memory or cache used to store every little packet until it can be processed and forwarded (or discarded) to the right destination. A 4 port gigabit switch has 4 1000mbps ports, but the backplane can typically manage 2-3 times as much bandwidth so that no one port gets bogged down. This is helpful for peer to peer traffic like copying a file between two wired computers and leaving some capacity for devices using the other ports.
The second is access control. Wired networks, and Wireless networks face a lot of noise and conflict. Wired benefits from requiring a physical connection, nothing passes through without being physically connected, but even that can face collisions where multiple signals arrive at the same time (or too many arrive at the same time) and fail to get processed so must be retransmitted, the cache sometimes can't keep up with bursts of data.
Wireless adds exposure to any signal in the vicinity on the same frequency. Think of AM radio in your car, and how stations bleed over each other at greater distances. Where radio lacks data to identify the source of a single, WiFi and ethernet have some identifiers that allow the access point (or router) to filter out signals that don't belong on the network. But, it all hits the radio receiver at once and gets queued to be filtered. Too much and the queue flushes and requires a packet be retransmitted. So, anything you can do to minimize signals hitting the radio will improve your network speeds.
What are the things that hit the receiver? Anything with a signal in the same frequency ranges. 2.4Ghz WiFi is particularly vulnerable. Radar, Microwaves, wireless home phones, bluetooth, wireless keyboards and mice all transmit signals on frequencies that might match the WiFi signal frequencies. So, every signal sent to and from these is in the air, will be "heard" by the access point, and analyzed to determine if it is noise or legitimate. That not only delays legitimate traffic, but can cause temporary outages. Queues to manage this are limited and data packets expire after a short duration. Apps monitor for acknowledgement of receipt of a packet and failing to receive an ACK in time will force them to retransmit a packet, adding to the congestion.
All of this to say, anything you can wire takes stress off of the network to process more legitimate traffic. Wiring devices, avoiding frequencies in the same range as neighboring networks, using 5Ghz on devices that are capable, even creating a faraday cage around your home to block signals from neighbors (ok, that may be a little extreme). Obviously, wired connections are an easy way to offload some congestion if reaching the location with ethernet cable is possible.
