I'm sorry if this has already been mentioned, but if you are getting 2 Caiques, you are better off with one of each sex. Caiques can be difficult to breed so even if you have a male/female pair, they are not always going to want to or even try to breed. I know my male hates other male birds his own size and has attacked a couple.
I know most people who keep them in pairs keep them in male/female pairs. 2 females can get very aggressive with each other as well when they reach sexual maturity, but it really does depend on the birds themselves.
If you get two, just be aware that if they are the same sex, you may have to separate them when they get to be mature.
Caiques are such active, playful birds that they do prefer to have another to play with, though it is better to have another Caique since they can be other species aggressive as well. Playing with a Caique the way they want can sometimes prove difficult as they are beaky, but when they play together, they understand each other's limits and can play rough without hurting each other normally, when for example a pet Caique bites us in play, it can be too rough and we ask them to play nice, a Caique buddy can tolerate the roughness and will dish out the same right back
