Screwed in solid inserts aluminium and bronze, wire thread inserts (helicoils), welded in aluminium inserts - all good, which is best? No idea.
What I can say is that pressed in bronze inserts are a bad idea. My head came with these fitted. One of them came out still attached to the exhaust pipe. The head had cracked around the port. Took a lot of welding to fix, aluminium inserts were welded in at the same time, they've stood up pretty well so far but I must admit the screwed in bronze ones look nice.