I prefer Colemac over Dvorak - because of better similarity with QWERTY and especially for CTRL+C/CTRL+V shortcuts!
Paper about Dvorak - concludes that studies about Dvorak superiority is not reliable! There is no proof study (all are related to Dvorak himself or does not confirm Dvorak layout efficiency).
I think that higher speed of writing is not the only one criterion - I like also the comfort of less fingers moving, which is undisputable (see analyzer below).
Links
- Keyboard analyzer based on written text: http://patorjk.com/keyboard-layout-analyzer.
- Czech writing course nedatluj.cz (for QWERTZ, but I wrote the userscript for Colemak)
- Yuhů's notes (in Czech)