@Jason W. I love these questions, because I don't know how one can make a decision when suggestions are given without any hard data as justification. I sure can't.
You mention "high growth" and "good positive cashflow." I am going to assume you are saying you want a growth market (good fundamentals) but can still give you some positive cashflow - in other words you want both but prioritize growth.
I put a chart together from Census and BLS data from 2010-2019, used to compare different MSA. I included the cities you mentioned, plus a few more mentioned so far in this thread. I take "Growth" to mean demand, which is population growth, along with a corresponding job growth. And ideally, those jobs a good high paying jobs, meaning income growth (which allows people to pay more for housing). However there is also supply side, which I take to be permits pulled as a percentage of existing housing units, and general affordability (median income / median house price), the higher the ratio the more people can afford to pay for housing. That's the general idea behind the chart.
The following is my own opinion to help describe the charts, but that's all it is - my own interpretation. I am not saying any are good or bad markets, the question to ask is - do they meet your goals/criteria?
Austin and Nashville look like high growth, Memphis and Philly not so much. Comparing Nashville to Austin, looks like they have comparable affordability, with more permits (supply) being added to Nashville. Therefore at first glance it appears Austin has the better supply/demand growth metrics, of the markets you listed in your opening post.
Some other markets commentary: Colorado Springs has a good mix of growth and balanced supply, Phoenix's growth seems to be outpacing the permitting, and Columbus though lower growth also looks pretty balanced.
I think it's also worth to take a look how the markets have handled 2020 job losses and recovery.
Most node-dived pretty hard, but if you compare Memphis vs Philly, which has comparable job growth numbers at the peak, looks like Memphis has essentially recovered whereas Philly is flattening. Nashville and Austin have high job growth and look to be recovering well, Phoenix less so.
Last thing I'll mention is a concept of "shadow supply" or potential hidden supply to come on the market due to fallout of foreclosures from 2020 and moratoriums, as described by Ken McKelroy. This is not a prediction, it's just looking at data and trying to take your best educated guess. Check out his videos on youtube, and here is one of the links he provided.
U.S. Foreclosure Trends | RealtyTrac