One of the questions you'll need to figure out for yourself, is what do you want this "dash camera" for. Vinny brings up a good point. The dash camera he recommends has a waterproof DVR. You can put that on your handlebar, or wherever and it'll be safe.
I didn't worry about that. Mine is stored under the seat. While it isn't waterproof enough to take scuba diving, it is enclosed in a rubber sleeve that keeps it safe and keeps the case from being damaged. I ride in Seattle, so this dash cam gets exposed to rain a lot.
Dash cameras have improved in resolution to the point they are about like what action cameras used to be like. In other words, pretty good. Since I bought mine for recording when someone hits me while texting, I really use mine as a dash camera. It's "install and forget"...and hope you never need the recorded videos for an accident.
Wi-Fi is great, but has limited usefulness. You're not going to be looking at your smart phone (or the screen for that matter) while riding. It's good though for the initial aiming of your cameras.
I think you'll find several cameras that are all good. All these so far have 1080 resolution. All have waterproof cameras. Ratings on Amazon look about the same. I know the customer service with Halocam is great. I had an issue with the first camera when they were just getting started. I was sent a new camera immediately.
The biggest issue you may have is with the memory card you buy. The SanDisk Ultra cards are good. DO NOT BUY the Samsung EVO cards. They can't handle the data throughput.
Good luck!
Chris