Ask HN: Get a Visa before apply for a job?

I'm looking for opportunities in the USA: my goal is get a job oversea (I'm Italian) to move there for few years and engage an American girl I'm currently dating. I was wondering if it's better get a Visa, wherever possible, before apply for jobs or try to get one after found a concrete opportunity. I'm thinking that the second option will limit my chance since it will require effort from the company. So far the USA Visa process is not really clear to me, with so many different options, so any help is appreciate to understand which one to look for. The option to get a Visa via my girlfriend is not available now, hopefully it will be in three-four years.