I wouldn't let that dictate your choice. Both routers have four ethernet wired ports for connecting up to 4 computers simultaneously. Keep an extra cable plugged in and wire the laptop when you are doing lots of big file transfers it will always be quicker. If its files often but not in bulk you wont notice a significant difference.
Linksys are known to make solidly functioning equipment (if plasticy in casing as noted above) that works out of the box.
The Buffalo one sounds great if you upgrade it to the non-oem firmware mentioned in the Newegg reviews. I'm unsure if Buffalo then give tech support once you have done so but as they allow you to do that then maybe they do.
They are probably on a par for your purposes because its unlikely your lappy will make the most of the Buffalo.
Neither of those replaces the modem. You just plug the modem ethernet into the WAN (wide area network) ethernet port of the Wireless Router.
You can buy all in one modem/wireless routers but whether or not your internet service provider will function with them or support them is something you would need to check - if they gave you the modem.