As a computer guy and a gamer, I've always preferred a solid wired connection. However, with wireless technologies such as 802.11n that isn't really that big a deal any more, even 802.11g is still suitable for good gaming.
Your ping times will definitely suffer a little bit when playing wireless instead of a cabled connection, but it won't be a bad choice. If you value a slightly (very small increase here) better reaction time, then a wired connection is the way to go (as in the case of first person shooters, fighting games, etc) but if you're using it for things like NetFlix or streaming media/downloading DLC, indie games, etc. Wireless will work just fine.
Edit: I just looked up the specs for the 360S, if you get a wireless router capable of broadcasting at 802.11n you won't have any problems (assuming you don't have any other major types of wireless interference [a cordless phone doesn't count]). Just make sure that you set up your wireless network to broadcast on a channel that isn't in use nearby. The standard channels are 1, 6, or 11 because they allow for the least amount of overlap if they run into another signal.