Rats make great pets, I currently have two (they should at least be in pairs) but have had over 100 at one point in my teenage years, had to convert a wardrobe to house them all.
Females are meant to smell less than males but I have had both and to be honest if they smell just as much as each other, the key is to clean the cage often.
I clean the entire cage every Sunday and change the bedding every second day, as my rats like using the bedding to urinate in occasionally. They do get out of the bedding area to use the toilet but it seems at least one of them is lazy and pees the bed. Also give them a corner in the cage as a toilet and they will use that, so they are quite clean that way.
Male rats are way more chilled so will probably be better for younger kids as Females tend to be more jumpy. Rats never bite unless you properly give them a reason to they are very submissive and would rather squeak and run off over fighting back.
They can live up to 3.5 years though so a bit longer than the 18 months previously quoted.
They are very intelligent and love to be interacted with usually first thing in the morning and at about 6.p.m if they are left alone they will just sleep until something interesting happens.