A couple of the best singer-songwriters around are both playing on Friday, so a choice will have to be made. Rodney “The Houston Kid” Crowell, one of the most successful musicians to come out of the Bayou City, is at the Heights Theater for a solo that will (probably) feature songs from his latest album, Airline Highway. Over at the 713 Music Hall, it’s Jason Isbell and the 400 Unit.