318 and 360 small block question

Both are great. They will both weigh roughly the same and are virtually identical on the outside. The 360 comes with 42 extra cubic inches so it will have more torque and is probably the better "bang for the buck" motor but the 318 won't be far behind it. In my opinion, whichever one you can get easier will be the way to go.
What kind of "build" do you want to do? If you just want to warm them over then both will hit 300hp easily. If you want 500+hp then the 360 will get there easier because of the extra cubes but by that point you're likely doing a serious build anyway and either motor is capable of getting there