Cleaner quoted by the hour vs flat rate

Trying to get our place cleaned every other week and the quotes are all over the place. One person charges hourly, another gave a flat number without seeing the house, and a third wants to do an initial deep clean first.

I found a couple more cleaners through InstaService, but before adding more quotes to the pile, which pricing setup has worked better for people long term? Mainly worried about an hourly job slowly turning into four or five hours every visit.