I'd place high importance on the employee state to the state you are hiring them out of.
Some states are a nightmare to deal with. For example, NJ, CA, NY and OH. Once you are registered in X state, your company is fair game to be pursued for any kind of perceived (lack of) compliance by that state, long after that employee has left you for another job. For example, you could earn a large fine for not filing to report you have no staff in the state.
States that I found were lovely to deal with were ID, TN, and TX.
Generally speaking, its highly recommendable to hire employees from your state only for this reason. I would not hire unless you are absolutely needing to.
You could be on the hook for a large tax bill since you have to write off developer expenses over 5 years – this is true whether an employee or contractor.
Hopefully it will be repealed* – but if not it is one of those things that no one would expect to exist since it is in the words of Senator Wyden "stupid."
https://www.law.cornell.edu/uscode/text/26/174
* edit It won't be repealed but a law can be created to ignored it until a future date. Once on the books, because of accounting, it is very hard to remove a tax law.
And besides, this information makes me even more happy with an opinion I already have - isn't that what the internet is for?
Employers of record ensure compliance with all local laws and basically just bill you the employee's fully loaded cost, plus their service fee