Great question — answering as the UphillTech team:
I would go with the service first, then location, as suggested. Google for example is already very good at localizing where a search is from and serving appropriate results. People for example are adding 'near me' less and less to their searches as people are realizing they don't have to anymore. That being said, what I would do is to test out your specific industry by trying out various examples in different cities. So if you are a plumber, compare 'las vegas plumber' with 'plumber in las vegas'. Do that for various cities that are a similar size to yours and see if you can spot any patterns that come up. No hard data to back that up, but many years experience as a local SEO consultant.
Full answer by Yan Gilbert: https://webmasters.stackexchange.com/a/111277 (CC BY-SA 3.0).
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