Colemak all the way.
I spent about a month learning Dvorak; I liked the idea of it, but it just never felt right. I experimented with some other layouts, but never seriously. Then I tried Colemak and it clicked almost immediately. As soon as I got to 30wpm I switched permanently and never looked back. It just feels right to me.
A year ago, I was typing 45wpm on Qwerty. Today, on Colemak, I average 60-70wpm.
Well, if we want to compare speed increase, 80 to 160 in a year?
But in actuality I think that this post best shows how arbitrary it is for layout; there are just feelings that you'll get typing on each layout, and one will suit you more than the other.
+1!
I find it's quite a personal thing. It can be a problem when someone tries a few layouts, finds the one that suits them and then simply states that that one is the "best".
ALL layouts have some compromises and sometimes even if the metrics show one as being worse than another, it will "feel" the best to someone, and that's what matters most.
It's nice, however, if people can give the reasons they like a particular layout most, since that can help others to decide if that layout is worth trying or not.
I like BU-Teck / AdNW because it gives a nice alternating rhythm to typing, all the vowels (and vowel-like characters such as Y and H) are on one side (like Dvorak), the most used characters are on the home keys, there is a good balanced finger usage (index and middle fingers do most of the work) and it's very different from QWERTY (which can be both a good and a bad thing, but in my case it means I can learn the layout without affecting my QWERTY skills which I need for everyday work). I have managed to relearn the edit shortcuts without a problem (Ctrl-C, Crtl-V, etc).
Dvorak, Colemak, Workman, Norman, QGMLW (Carpalx), etc. are ALL better than QWERTY and IMHO it's worth learning one of them if you use a keyboard often, although that's another personal thing. For some, it's actually not worth the change (they don't use a keyboard enough to justify the unlearning / relearning effort or they have used QWERTY for so long that they just don't want to change or would take a very long time to see a benefit from another layout).