I wouldn't say British comic book writers are better than American writers. The two biggest names tossed around from the UK tend to be Gaiman and Moore, who are almost universally loved. Beyond that, you've got a real mixed bag. I love Warren Ellis, but he's hated by 80% of the X-Men community. Grant Morrison gets a lot of love, but there's a bit of a mixed reaction to his current DC work (god knows I never feel satisfied with his endings and I still disdain his X-Men work). Mark Millar really is a hack, like hunter said. Mike Carey went from the most praised X-Men writer to pure Rogue fan fiction.