GX 1200 a15 or a14

gx

depends on the application.....power, economy, high reving and low reving.

Well that's a very loose question.

For a stock A10 that sees 10 hour days running a small generator & economy of operation is a must, then the round port A10 or 1200 head.

For a budget high performance A14 or A15 engine, then the original A14/15 head [same specs]

For a well developed A series where cost is not really important, then 1200 GX on a 1200 block or if a 1974 or later A12/14/15 block, then either the 1200 GX or the B210/120Y GX head would be fine.

For a balls to the wall racer, the Nismo competition head is the go.

So, ... what's your application?

A GX head's valve seats can stand being opened up to accept the larger A14/15 valves, for around the same cost as having the seats recut in the standard size.
GX=FTW