Since I've been losing weight over the last year (with some stalls here and there where I got off track

), I've been getting more into exercise. I've always picked sneakers from what was on sale at the sporting goods store, but I've been thinking about getting a better pair of sneakers.
First, do the different types of sneakers really make a difference? I'm expecting to hear both ways on this one.
Second, I've mostly been a brisk walker, but I've been building up to where I can jog more than walk (5 mph vs 4 mph). This is just in case it matters in the shoe area. I'd like to possibly build up at some point where I can run, as long as I find a better supporting sports bra. Ouch!
Oh, and third, 90% of my walking/jogging is done on the treadmill.
So what kind / brands of shoes do you guys recommend?
Thanks!