Two ratties would need a cage of at least 4 square feet I believe, with lots of hammocks and toys in it ^^ As too whick sex is easier to tame, it really depends. My girlies adapted very well and girls are generally more active and like to play with you then boys, but it depends on where the rat came from and how it's been treated. Cages are better than tanks because you can hook ratty stuff on them, and they have more room and ventalation for the rat. Most guinea pig cages have wire bottoms, and if that is the case than it is diffenatly not suitable for a rat. Rats need solid-bottomed cages to be happy and healthy. Are you getting your ratties from a pet store or breeder?
Most guinea pig cages have very spaced out bars, most adult rats can fit through a 1"x1" opening, so be very wary of bar spacing.
I detest tanks and aquariums, rats produce a very large amount of ammonia and it gathers on the tank walls, contaminating the rattie's air supply.
That, and where will you hang the toys?
There really is no 'taming' rats, they love human company no matter what. It just depends on what you want from a rat.
Males(if neutured) tend to be lazy, snuggly laprats. My boy loves sitting in my lap on his back to have his tummy scratched.
Girls are very active, and love games and toys. My two current girls live in a extremely large cage(a ferrret could live comfortably) with toys and ropes and hammocks but still get bored and love to come out and play with me.
girls, however, are extremely prone to tumors. Most are harmless, but some are fatal and painful for your rat. If you get a female, it's best to have her spayed to reduce the risk of tumors.
Yeah tanks and aquariums are the last thing you want to put to rats in. When My boys were babies I had them in a huge tank I had and it was just too much work to clean and it just wasnt any fun. Like Vixie said, ammonia is a big problem when it comes to keeping rats or any animal for that matter in an aquarium, so unless you keep it clean I wouldnt keep them in there. Right now my boys are in a very large Bunny cage, which is fun because they have hammocks and things hanging around everywhere!