The 69$ Apple TV 3 supports 1080p from iTunes and Netflix. It has Bluetooth. MicroUSB (For service). HDMI, Infrared Receiver, Optical Audio. It has 10/100 Ethernet and 802.11 a/b/g/n. It has 5.1 Audio
The 149$ or 199$ Apple TV 4 contains 32GB or 64GB of Cache. I saw statistics that show it as only supporting 1080p but I think I heard it supports 4k. Bluetooth, USB-C (For Service), HDMI, Infrared Receiver. It has 10/100 Ethernet and 802.11 a/b/g/n/ac. It has 7.1 Audio. Siri Remote and App store access. A Lightning cable for recharging the remote.
When it comes to the physical differences between the 3rd and 4th generation tv, one has a matte black and one has a shiny black. The 4th generation is a little thicker and also has a black remote that allows you to ask siri questions and to perform tasks for you. The third generation remote is silver or chrome (I don’t know what its considered)