Wifi is good enough for most mining operations. I have used both wifi and ethernet cabled connection for mining and I hardly notice any difference at all. You can perfectly safe go with wifi for your mining rig.
It is always better to choose wired, wired is definintely more reliable than wireless, with wireless sometimes the connection lost and by that you may missed the chance of mining or wasting your time while you are away and cant monitor your rig.
Also wired connection tend to be faster than the wireless ones so the choice obviously wired ones just for more reliability.
It all depends on the quality of your router, the quality of your wifi adapter in your computer, how far the distance from your router to your wifi adapter, how many other wifi networks around in your area.
If all those factors are good, there is hardly any difference between wifi and wired.