I use a gillete fusion as well. My best guess as to why they're so popular is because gillete gives you a free razor on your 18th birthday (or at least everyone I know got one). They'll make it up on the packs of blades, which are like 5 or 7 bucks, I can't remember.
As for disposable razors I haven't had too much trouble with Bic's comfort twin razors and I like to take them when I'm traveling. They're pretty cheap.
