The best place to buy and hold is where you can :)
1. Look at employers in the area - you want some diversity of employment so that if 1 company closes you don't lose a bunch of the population
2. Look at population/migration trends and futures. Read the census.gov site and do a few searches. You want areas that are trending positive for population growth.
3. Neighborhoods matter, even a few miles can make the difference between good and bad deals. Get to know the specific neighborhood, RE is hyper-local, there is no single market in any metro area, it is comprised of many micro-markets. This matters.
4. Deal specifics of course are a big deal - define your buy box and make sure the specific deal works (cash flow from day 1).
Best place to invest is where you currently have a competitive advantage, or where you're willing to put in the work to create a competitive advantage.