(Yesssss I want to hear it :3
I think the rivalry will work well, cause I can only imagine Sherlock forcing the hat to put him in Gryffindor so he's with John but he won't know where John definitely will be cause John is after him in the alphabet. And they'll have loads of time - they have like four classes not together (herbology, history of magic, flying and astronomy) which are the ones with the least periods. Also different houses mean we can keep the sneaking out every night and making a kind of secret base plan xD)

Sherlock was listening even less than John was, spending his time glancing at their fellow first years and mentally sorting them into houses. He spotted Molly almost immediately, who he of course already knew through their parents being friends. There was no chance that they would be sorted into the same house. Thankfully. She was a bit clingy and he didn't really like her. She wasn't interesting. Really none of this bunch were interesting. Some looked like they would be annoying, nuisances, but none were interesting. Well they weren't as interesting as John. But Sherlock didn't know anyone else as interesting as John. He glanced to the side, smiling at his friend. He could tell how excited John was and it was rubbing off on Sherlock. 
"Want to go in a boat together?" Sherlock asked in quiet whisper as everyone started pairing off and heading towards were the boats waited. He could see Molly searching for him and really really didn't want to go with her. He wanted to go with John.