For the wii either will be fine, but for your PC both will slow down your connection ( download ) speed noticeably. I currently use security based on MAC addresses. If you don't have the address on my list you don't get in. I also have my SSID broadcast turned to off.
This will only mainly allow people who are really trying to break into my network to get in, I say if they are trying to get in in the first place, they will get in no matter what.
For the wii, nothing to worry about in my mind.
Hope this helps.