Do I notice a difference when switching brands? I sorta do...but I think my days of experimenting with string companies are over, so I just go between Ernie Ball and D'Addario and I find both of those pretty similar in feel and tone. DR is something I've toyed with off and on years ago, and I think they were a bit on the stiff side, but they tend to be more expensive than the others and I can buy 25 set packs from D'Addario, so that's kinda the dealbreaker. So, these days its just either 9 or 10 XL's, just the basic ones, nothing special. I was using 8's for a long time, but lately I've been using Eb tuning, so I need a little more tension. I also got a nice deal on a box of 10's, so figured...why not?
However, there are two particular string brands that I dislike.
Dunlop. I never liked anything from Dunlop. They always break and sound off to me.
NYXL. I know these are supposed to be the premium D'Addario strings, but I don't see it. I tried one set, and they were so harsh sounding, I couldnt use em. I had to let them sit on the guitar for to weeks before I got any usable tone out of them. Never again.