Tfs powdered metal guides are a huge plus IMO. I've been researching the heck out of heads for my own car for a few months now and I came to the same "afr or tfs as cast 220" conclusion. What ultimatly swayed me was the pm guides. Venders offer them for 100-125 extra over what the tfs cost normally. Power to the ground between the two heads is within 10whp unless ported and I'd gladly give up 10whp to not have to pull heads and replace guides as a common wear item every 20-30k miles (if that?)