User blog comment:Ficus7/Allowed Technology/@comment-11135771-20140913133317/@comment-11135771-20140913153608

Well, there are a few differences in functionality. In the extremely long distances seen in space battles, laser weaponry has a bit of a speed advantage since the beam travels at the speed of light, whereas particle beams are made of, well, particles, and thus are at least a little bt slower (though at the ranges you would see for naval/air battles both are effectively instant-hit). Lasers are also probably better for burning and cutting, but you need a LOT of energy to make them effective as weapons since the heat of the beam is what does the damage, as opposed to the kinetic energy plus heat of an ion beam. Thus, an ion beam would probably be a fair bit more powerful than a laser weapon using the same power source. I'd also expect that laser tech might be less expensive to outfit ships with, seeing as we almost have laser weapons even today, but as far as I know there haven't been any functional ion beam weapons constructed (except maybe Tesla's death ray, but I don't know if the prototype of that was actually built, or just designed).

This is mostly just speculation though, of course, since we don't have any giant laser weapons or ion cannons in existence currently.