Wifi is not that bad, but using an ethernet jack is 100x better so bring one. Wifi is bearable when you are studying in the lounge while ethernet is a MUST when you are using your laptop within your room.
Routers are good options too just make sure its security protected so you don't have people stealing your wifi. When I first moved into my dorm in September the WiFi was atrocious and only worked in common areas, but within a few months they redid the WiFi and it now works very well in all of the rooms.
What I would recommend is to for sure bring an ethernet cord, and then if you move in to the dorms and realize you don't have WiFi in your room buy a router for convenience.
I live in Foothill, and we have no WiFi in my suite. Ethernet cords are essential, and yes, you need to bring your own. We use a router in our room, and the WiFi speeds are a bit slower than the ethernet speeds, but not by much.