Im so glad you are looking into rats, they are really really great pets. As much as I love my guinea pigs, my preference for a small animal has changed dramatically since owning my two rats- Jasper and Jinx.
Both my boys are super friendly. They both come to the cage door anytime I go by and LOVE to come out and play. Jinx is more of a cuddler, while Jasper has different moods- Sometimes liking to cuddle, sometimes wanting to play. In general females are more active while males are more cuddly (although all babies are playful).
I would honestly describe a rat more like a tiny dog than anything else. They are very loyal. Both of my guys are being trained to ride around on my shoulder.
Jinx went to the store (party factory) with my and slept in my hoodie pocket most of the time.
My favorite 'game' with them is hand wrestling. I softly pull my hand over their fur backwards and then they run away and run back full speed to jump on my hand.. They could do this forever.. its really fun.
If you have more questions- feel free to ask!