The difference between male greens and female yellows are pretty minimal size wise. Female yellows will be somewhat thicker then the males. Don't count out male yellows either. One of my favorite and best behaved annies is a 7ft. male yellow.
Temperament differences depend on the individual animals and to a certain extent, where you get them. There are perfectly behaved and really nasty examples of both species. Obtaining a multi-generation captive bred animal can increase your chances greatly of obtainig a mild mannered critter. They all tend to be a little nippy as newborns.
Keep in mind that greens do have a little tighter heat and humidity tolerances over yellows so do your homework BEFORE you buy so they are taken care of properly once they arrive home. As mentioned, try to buy a captive bred animal from a reputable breeder or at the least a captive born one from a decent dealer that has them feeding on rodents. Staying away from female greens, which are the only ones that can reach the enormous size, is smart thinking if you're not ready for it. Of course an 8-12ft male green or female yellow is still a formidable animal and demands one's repsect. Read and learn all you can about them first then see what's available to you for purchase. Ultimately the choice is yours and you won't be disappointed in either one.
