I can help you a bit, based on my experience.
All low voltage lights (12v), require a transformer. At the very least, this makes initial cost higher than others. They do generate a lot of heat, and as such bulb life, I've found, is quite short. They are not a fire risk, fitted correctly, but they must be fitted correctly. I've had transformers fail, as well, so that's more money........
Mains voltage (240v) lights are in several types: Halogen, CFL, and LED.
My experience is that the halogen lights in 240v suffer the same issues as the low-voltage halogen: heat & short life. I have found CFL to be only so-so, light quality wise, and I haven't found them to last particularly long, either. At least nothing like I expected.
Which brings us to 240v LED's. I am currently retro-fitting my house with these. They have no heat issues at all, they are 1/10th the energy requirement, and they are inherently long-life. They aren't cheap, but there again I won't have to chuck the bulbs every few months, either, so it should more than balance out. If you've a lot of them, there'd be a noticeable reduction in energy use. But, and there's always a 'but' - you need to buy at the very least, 2W, and preferably 3W units to get good light, and you need to see them on, for colour. Some are noticeably 'artificial' in light colour, and others spot-on, colourwise, and look natural.