The B20B or F head would be my choice. The biggest problem with using the B18 head is that you won't be able to convert it to run on unleaded because the valves are too close together to allow stellite exhaust seat inserts to be fitted.

Compression is over rated, it gives a rapidly diminishing return as you increase it & it makes the engine much more sensitive to accurate ignition timing & poor fuel. Unless you are building a pure race engine, you are better off leaving compression low & using low octane rather than paying the extra money from the best fuel.