I wouldn't break up a pair, ever. Trying to bond with a Macaw who has been taken away from his bonded mate (even if they are the same sex) is very unfair to the bird (both of them), and would be very difficult to win over. As far as the better choice a B&G would be a much better choice especially for a beginner. Scarlets are much more prone to bite than a B&G, although I'm sure some Scarlet owner might disagree. I personally don't recommend a Macaw for a novice especially a rehomed bird who may have issues. If you still want one of those birds, visit with him many many times before bringing him home. After many visits you will find out if you have a good chance of the adoption working out. Good luck.
Willist is correct. Pairs should never be split and I am very surprised the rescue is willling to do this. Macaws (all psittacines, in fact) are monogamous and mate for life, splitting a pair is a cruel thing to do to a poor animal. You are doing a great thing by rescuing a bird instead of buying one (which only contributes to the huge overpopulation problem and lines the pockets of people who exploit animals for money) don't 'dirty' your good deed by splitting up a pair. Plenty of single birds out there in need of a good home.
This all makes sense. I dont know for sure that they would split up a pair or not. thanks for the info.
Really glad we found this site, lots to learn from. thanks again