Kelsie said it all! Girls are fun to watch, and not so hot about cuddling until they are older. Females suffer from tumors more so than males. Males are more laid back, and love to snuggle up, and take soulder rides. Males however have massive testicles, unless you neuter then, and this is a problem for some people.
I run a rescue for rats in Ontario, Canada and there are SO many in need of rescuing, so consider adopting! There are some GREAT rescues all over the US as well!
Make sure you've got a nice BIG cage, like GP's they need lots of room, and you can usually find a ferret nation cage on kijiji for not a lot of money, a half of a ferret nation is good for up to 3 males, and 5 females. Females run on wheels day and night and amles love their ham,mocks!
Rats make wonderful pets!