To be brutally honest; Chrome.
Yes, I said it. Chrome is worse than IE. For a start, it's slow as hell compared to FF, it feels zoomed out and you can't zoom in or out with the trackpad. It's also clunky when it comes to scrolling with the trackpad. Scrolling with the trackpad is easy on FF, but pretty much harder on Chrome due to how unresponsive it is. I don't understand where all the praise comes from; it's slow, a bit clunky, and doesn't remember passwords as much as other browsers. I'm gonna sound like a hipster in saying this; but Chrome is annoyingly overrated.
I think I'll just say it out loud why I think Chrome is pretty bad when you think about it...
Horrible accessibility - it does not respond at all to Windows accessibility settings, and it doesn't use standard dialogs, so keyboard usage is not optimal.
Unresponsiveness in general - seriously, the Android browser runs better than Chrome on the same tablet. Chrome just paints out or sits there on my tablet so much, I quit using it. The benchmarks? Turns out (as I've always suspected), they mean nothing. (There's a reason how IE9 is still fast enough after over 18 months. If you are great at something, you'll be great at that for a long time. As it turns out, drawing graphics of real sites and refreshing it is more important than speed benchmarks.)
Shoddy text rendering - GDI+ rendering is not ideal these days. Windows ClearType on the old drawing API means really jaggy, uneven text. When you're used to properly laid-out text, smoothened in IE, Firefox, and Safari, it's hard to go back to that. It's very obvious with large type - Chrome even cheats by turning off subpixel rendering on Windows!
For a browser named "Chrome", it sure has quite the thick, visible chrome... Hmm...
There's a reason why Google Chrome is not yet installed on my laptop.