Welcome to the forums. You're talking to other customers here.
Rev I. is the latest. It has more memory, a faster processor and GigE wired ports. It is 802.11n vs. 802.11g on the rev F. This bumps WiFi from 54Mbps to 130Mbps. Range, however, takes a hit. You can read the details here:
You can buy it here for $74.99:
Or buy something better that supports 5ghz band and 802.11AC. Note even the latest Verizon actiontec only supports the 2.4ghz band with 802.11b. 802.11g, or 802.11n. Note if using FIOS TV you will probably need to keep the Actiontec router as well.