Classic armies in Mk 4

Getting back into the game and just trying to understand how well legacy armies fit into Mk4. Do many people play the unlimited format, or is it pretty much just prime? Are legacy armies still competitive at all or are my Trollbloods in for a bad time? What are some general tips in list building this edition? Is it Infantry like Mk 1 and 2? Is it super solos like Mk3?