Hey Jane! Like you said, there's quite a bit that goes into that question, but I'll throw out a few key points. I sold investment properties in Nashville and now DFW, so I can speak a bit on both of those mainly.
1) Spend a day and research the STR regulations in each location. I believe it was in 2021 that Davidson County (Nashville) began restricting who could receive a permit for an STR. If a property already had one, then it would be grandfathered in. As for applying for a new permit for a property that you purchased, you can only do so under certain conditions. If you were to rent it out at monthly intervals, then it wouldn't need that permit anymore though. It has been a minute since I've been in this market so definitely do you due diligence on that one still, I don't remember all of the details anymore.
2) Cash flow is important of course, BUT that shouldn't be the main factor. I would focus on whichever market has been experiencing the most growth, as appreciation will be more valuable to you in the long run. If you can find a semi-distressed property, that would be ideal. Do a bit of research into the BRRRR method.
I know Austin and Nashville are two very good markets! Admittedly, I don't keep up with Santa Rosa Beach, so I'm not suggesting that it is subpar in any way to the other options. Find a couple properties in each location though and see which will be the best deal with these factors in mind. Hope that helps a bit!