If you are planning a release business then as long as you have birds well capable of returning home then you are ok
If you want the best type of bird then you are looking for busshaerts, logans etc but they don't have to be top racers as time is not important as getting home safely.
This is what is classed as a garden dove which we have in our dovecotes, the second picture is a barbary dove, totally different, no good at homing