Is the 383 a better engine, or does the 440 just have more displacement?

It really comes down to how much hp you want to make and at what peak rpm and powerband. So say you want 450 hp and have a idle - 5000 rpm make peak power around 5000 rpm. A 440 with the right parts will do that no problem. Now if you build a 383 for peak power at 5000 rpm and idle - 5000 rpm your gonna be around 400 hp
Or if you want the same power of 450 hp your gonna have to spin the 383 up a bit to maybe 5500 rpm and 1500-5500 rpm powerband.

So it all depends on how power and where you want it. If both built to the same powerband the 440 will make more power but need more cam carb head etc.. to get there. If built to the same power they will need similar parts but they will work at different powerband.

Eg. a decent built hot street engine can make 1:1 - 1.2:1 hp per cid so if a 383 can reach your power goals with in that range your golden or if not need to go larger.