Sorry, been busy in real life and didn't spot this one.
The degrees is beam angle. So a 45 gives a narrow beam, 60 gives wider.
The best really depends on your set up. Wider beams cover more of the tank with less lights but don't punch to the substrate to well and spill light more if they're raised. Narrower beams give more punch to the substrate but you need more to get the coverage without areas of light and shadow, creating a spotlight effect more.
It all depends on what you're trying to achieve, how high your light is going to be and what you like the look of.