In SF at least Grubhub tends to have some of the more "typical delivery" choices (pizza, chinese food, thai) and decent customer service, Doordash seems to have the most variety but the dashers take their merry time on their way to you (and customer service is nonexistent), Uber Eats is somewhere in between grubhub and doordash in selection and has nonexistent customer service (but at least give you a refund if something goes wrong), caviar has a smaller selection but a lot of unique/higher end things (along with a terrible app but OK customer service), and Tock is targeting the "high end at home" market. There's also postmates which seems more expensive than the others for the same exact restaurants (but seems to have more traction in LA).
At the end of the day, the search is really bad (clicking the healthy category includes deep dish pizza and fried chicken on almost all the apps), the drivers aren't adequately compensated so the customer experience is bad (your driver might make 4 stops on the way to you and your food will be cold), and the apps are slow and buggy.
I'm convinced that significant improvements in search, recommendations, adding proper review support, and finding a way to not piss of restaurants in the process will determine the winner in this battle. The differences in selection are too small (in SF caviar which is owned by doordash and tock being the exceptions) to really crown a winner on that front.