There are a few differences between male & female rats. Remember all rats have their own unique personality and this is a generalization, so it is possible to get rats that do not fit into these boxes. It is important when getting a new pet to never go in with perceived notions of exactly the personality you want. All pets are unique!

Males:

• Larger than females

• You can definitely notice their boy parts (testicles), they are rather large & can be off-putting to some.

• Are more likely to mark (pee) on you and everything else.

• Are often more lazy and relaxed/chill than females. Males do tend to slow down quicker than females.

• Still, have to be kept in pairs or larger groups

• Have an orange secretion on their behinds called buck grease. Not all males have this, diet & hormones plays a large role.

• Some males once they reach maturity may end up with hormonal aggression. This usually happens around 6-8 months. It is caused by a shift in hormones. They will likely not outgrow it and it may even get worse over time. Many males will not have any change at all, but some will have a definite shift in personality. Your once sweet friendly boy may begin to bully or worse attack his cage mates, sometimes escalating to serious fights. In severe cases, he may even be aggressive towards you. Getting your male from a breeder who breeds for temperament significantly lowers the chance of hormonal aggression, as breeders make sure to breed away from it and monitor it in their lines. Neutering is also an option to prevent or end the issue (though comes with risk as well). Mating him will NOT help and may actually make it worse (as well as pass on his aggression to the babies)
  
   

Females:

• Slightly smaller, you will need to be more careful of bar spacing to prevent escapes

• Tend to be more active, energetic & playful. In my experience, they tend to be more exploitative, more likely to test boundaries & rat proofing and need far more mental stimulation. They do not always sit still & like to be on the move so may not be the sit & cuddle with you type, Though many females slow down with age. Females are still affectionate & loving and often enjoy sitting on your shoulders. They may be more prone to visit you for a moment, run off to do something else then come back to say hi. Many girls are still sweet & cuddly.

• Females do mark but in my experience, it is not as common and way less than the boys.

• Tend to be worse chewers (I believe it is because the ladies tend to require more mental stimulation & activity which they may not be getting)

• Females can be prone to mammary tumors. A healthy environment and diet play a major role in the prevention of tumors.
  
   

I enjoy both sexes quite a lot. My boys are so chill and I just can just pick them and snuggle them. Most are quite lazy, it will be free range/play time and I will find them all sleeping on top of their cage. They really make the most of it! ..
I do tend to really love the girls though. The petite graceful beauty. They are so smart and fun to interact with. They are always keeping me on my toes. They have so much life & energy. My girls are still super sweet and cuddly and yet are more full of life and energy. 

But I have had super hyper males and super lazy girls too.