As I said somewhere earlier in this thread, I live in DeWalt world, it works well for me.
My personal opinion is with battery power tools to some degree you get what you pay for. DeWalt do some cheap 18V tools, but along side these they do some which are significantly more expensive, they're not the same, fact! I originally went the DeWalt 18V route and it served me well, however now when buying I've gone 54V where available, they are amazing, but for occasional DIY use the cost justification may be difficult. But if I want to drill a 30mm hole through concrete my 54V DeWalt battery hammer drill is the way I do it (and yes I do it!) Even hanging a TV on a wall bracket the other day I used my 54V pistol drill, it goes through brick like no other drill, corded or battery that I've ever used before.
That all said I wouldn't dismiss 18V tools, I have a 18V impact screwdriver I use a lot, 6mm 150mm screw into timber, its like screwing into butter. An 18V 1/2" impact driver, removes plenty of things a breaker bar wont budge, the best of it when doing machinery installations where the machines are bolted down with large threads, what used to take maybe 2-3 hours with a ratchet, the 18V 1/2" impact driver has them all done in minutes.
One of my pals swears by Milwaukee, but as you correctly say
@Calimori they use more than one battery style, which I see as a little annoying.
Just recently got myself the DeWalt (18V they don't do a 54V and if they did the batteries would be too heavy) battery heated jacket, it's a nice but of kit, very welcome on the colder days we were having a few weeks back.
Pay your money, take your choice....
Chris.