In other words, if you're new to both then the main consideration would (in my opinion!) be:
- Would you ever be forced to use QWERTY keyboards (Colemak makes for easier transitions)
- Would you be using common keyboard shortcuts (Colemak preserves more of them)
- Would you be using other people's computers to type your layout on (Dvorak is usually pre-installed; Colemak isn't on Windows nor Mac systems - however, if you can use an USB flash drive in the computer there's portable solutions that are very nice I think)
- Do you prefer hand alternation (Dvorak's forte) or smooth rolling movements (Colemak's forte)

etc.

Asking the Colemak forum is of course looking for a biased answer. My own answer is bound to be: Hell yeah, use Colemak! I changed from Dvorak to Colemak myself and haven't regretted it a bit. But each to their own.