First time post engine rebuild advice please

The 360 top end will be a better choice at higher RPM's....the 318 top end will probably give you a bit better low RPM torque. There can be other variables depending on some of your other equipment, rear axle ratio, head castings, port work, etc. Whichever you choose, make sure that everything matches (ie. port sizes) so everything flows good. CC your old heads and compare to whichever replacements you choose to make sure your compression ratio stays where you want it. The bigger question is why the 1st set of heads cracked! Overheat? A/F ratio too lean? Detonation? No (or too little) spark advance? All needs to be checked before you toast another set!
Thanks, Mark