The question was slightly editted and clarified in the original post and some comments, so my original answer has been replaced and you can find it in the edit history if you were interested. I've ignore some parts of the original question, because it was too broad.
what are the advantages and disadvantages of... [a] 100 MW maser, laser or graser?
Masers may be generated simply and efficiently. We can do that well enough nowadays... something like a gyrotron is decades old design, and I believe we can get efficiencies of at least 50%, which is pretty good. The range of a maser is more limited than devices that emit shorter wavelengths due to diffraction issues.
(note that in really old scifi, masers may have been used simply because there were no lasers yet, and there was a time when lasers might have been called "optical masers")
Lasers (by which I'm choosing to mean "things that emit visible and near-visible light") are harder to generate (read: needs more clever engineering, generates more heat, etc etc) but have the advantage that they have a much longer potential range as they suffer less from diffraction due to their shorter wavelengths. We also have a good knowledge of optics, and there are plenty of ways to bend and focus visible light. Efficiencies are likely to be lower than masers, but needn't be terrible, especially in a fancy future scifi setting.
Grasers aren't quite scifi... bomb-pumped nuclear lasers have been around in theory for decades. The biggest problem with them is that as the beams can't reasonably be reflected, and any attempt to focus them is probably going to require something like a zone plate which means you either have to put up with unfocussed beams (read: short range) or losing at least 50% of your emitted power to the opaque bits on your zone plate. Efficiencies are likely to be very poor... maybe only a few percent. As a weapon, they might be found on nuclear missiles which can get close enough to the target to zap it, rather than trying to build one onto a warship.
what the difference is between, say, a 100 MW x-ray laser vs a 100MW visual light laser fired at a ship
There are a number of important differences. An obvious one is potential range... the radius of the focussed spot at the target (which you want to be as small as possible) is proportional to the wavelength of the light the laser emits. X-ray light has less than a twentieth of the wavelength of visible light, which gives a massive potential range advatange.
Both lasers, when they're in their killing range will generate plasma when they hit their target. For the visible light laser, this is inconvenient because the plasma will be opaque to the radiation it is emitting, and so the laser will have to stop, wait for the plasma to dissipate, and then start again so as not to waste power on heating the plasma instead of zapping the target.
The x-ray laser is under no such limitation, and can keep firing for as long as you like, and pulse as fast as is practical. The drilling speed of an x-ray laser at shorter ranges is likely to exceed the speed of sound in the target's armour. Each pulse of the laser will generate a shockwave in the armour, and these shockwaves will all merge together at the back face of the armour producing quite a bang.
At any range, an x-ray laser of suitably short wavelength will ionise material it is incident upon. This will damage the chemical and crystalline structure of the target (important for handwavium "thermal superconductors") and interfere with electrical and electronic systems.
X-rays are obviously highly penetrating. They have a measurable attenuation length in matter, meaning that the energy deposited in the target drops off exponentially with depth. This means that it may be possible for a beam to shine straight through thin or low density materials and cook whatever is underneath (eg. the meatbags flying the ship), even if it isn't actually powerful enough to melt the armour.
Finally, and this is perhaps the most important thing... X-ray lasers are going to be big, and they're going to be inefficient. You pretty much have to use a free electron laser, and those things get pretty hefty if you want small wavelengths. You have two choices... a linear particle accelerator (aka a LINAC) or a synchrotron. The former can be very, very long... the European XFEL is over 2km long, for example, though you could probably get away with a more modest accelerator a mere few hundred metres long. You can wrap this around into a doughnut-shaped synchrotron to be more compact, but whenever you bend the electron beam you will lose energy to synchrotron radiation, and that means lower efficiency, more heat output and larger power requirements.
You might think that you could use a super-compact wakefield accelerator (with accelerations to GeV energy levels over metres instead of over hundreds of metres), but alas current designs are not actually very efficient (certainly no more than 30%, excluding seed beam, FEL and optics losses) so again: more heat, higher power requirements, lower output. TANSTAAFL. Its enough to make you just throw up your hands in despair and just use a normal laser instead.
