I can't be sure since technology has so many different factors, but splitting a single Ethernet out into multiple with a network switch won't really affect it much if at all. Cat5e cable/jack (common for most cables) gets 1 gigabit, so unless you have a gigabit connection and maxing out the connections already, you shouldn't notice it.

As for WiFi, even though a lot of newer technology is great, it's not going to beat Ethernet.