Sessions would be good pick.
He had the guts to jump in very early and is well respected in Congress
Susana Martinez would be a good pick on multiple fronts. A woman, to help defuse the "Trump is a misogynist" rhetoric. Hispanic -- ditto on defusing "Trump hates Mexicans". Border state governor -- strengthens his immigration stance. Executive experience -- though not Congressional/DC experience which is a Trump weakness. West of Texas -- helps in western states
Sessions is my fav Senator. He is more valuable by staying in the Senate. Trump or any GOP nominee will pretty automatically get AL, and most, if not all of, the South.
I wasn’t big on Haley’s GOP response to the SOTU with not even thinly veiled shots at Trump right before primary season got going. She didn’t let up much afterwards, either. Wasn’t she a Rubio/#Never Trump during the SC primary?
Just don’t know enough about Martinez or Portman. But in my book, Haley is OUT.