Why choose those user who need 1 merit to rank up while you can give it to deserving users whatever merit score they have? Are you really want to help or you just want to be selective on your choices? It's a rare case to see a user to have 1 merit before to rank and better give your merits to newbies so that they will be inspired to do a hardwork here.
I agree with the OP. You can give merits to Newbies or someone who do quality posts. If you really want to give merits to those who need to rank up then you can check this thread -
https://bitcointalk.org/index.php?topic=5206035.msg53571791#msg53571791 where you can find the list of members who are in the pipeline to rank up. You can check their profile and help them to rank up.