Just as a simple test, 0mq.com redirects to zeromq.com :-) Also, if all three are evenly distributed, then that makes the letter prefix preferable to the digit

Just as a simple test, 0mq.com redirects to zeromq.com :-) Also, if all three are evenly distributed, then that makes the letter prefix preferable to the digit prefix 2:1. In any event, I think "0mq" looks ugly and people might mistake it for "OMG".