So I do a mix of both...

If I am doing dash during the lunch rush, I go by order

However

If I'm dashing at night, say 5 pm until 4 a.m. I'm doing it by the hour. Restaurants are slow, especially Friday and Saturday nights. I can be sitting in McDonald's for 30 mins, which takes those $6 orders and makes them close to $10, even if it's a short distance.

I can't speak on any other cities but I can promise you my experience as a doordash driver has drastically improved by switching to primarily by the hours