I live in Sunnyvale and spend most of my time around the South Bay & Peninsula. I left AT&T a year & a half ago for Verizon and at the time, AT&T's 3G data was certainly faster than Verizon's though Verizon seemed to have a more consistent connection. Call quality on AT&T was horrible though; this is why I jumped ship for VZW. Having said that, I'm not sure what AT&T's HSPA+ or LTE is like for data around here; obviously decent from what the posters above said. Verizon's LTE coverage around here has definitely impressed me - not only are the speeds excellent (anywhere from 10 to 25 down generally) but my Iphone battery seems to go alot further as well since it's not stretching to keep a tower connection and the call quality is good as usual. I can't speak to what AT&T's network is like now but my general experience was great data speed but good luck keeping a call. Hopefully, it's improved since then.