Soz, that I had to post this here, but my comment wouldn't post in the comment section (sigh)
Uuuuuuuuhhhhh *climbs into trashcan and cries for three years*
Tbh, I would like to say Derek and Rahul because Derek has kinda always been cute and kind and Rahul seems to really like him. Derek's also ultra hot and that's a plus, however, I feel that he's too innocent and nice. I still ship Rahul and Peter way more because they had a good history and Peter seemed really driven to get Rahul, at the beginning. Peter, to me, is also a lot more of a wholesome character (wow that makes him sound like bread), but I mean it in that we've come to know a lot more about who he is and where he comes from. Tbh, Derek is shrouded in a certain degree of mystery, and that is enticing, but makes him a character that I don't completely trust with Rahul. Ya, I know Peter cheated on Rahul, and I don't condone cheating, but they were university sweethearts. And that's at least worth an extra 50 ship points.
In terms of Rahul's attitude to them, I feel that Derek got it easier than Peter. Peter really had to work to get Rahul's jelly and that made me like him quite a lot, the fact that he was so devoted. Derek had it easy and that makes his relationship with Rahul volatile because it was built very quickly and can crumble very quickly. I still think that Rahul loves Peter despite how much it hurts him to love him. I really like Derek, I do. He's the equivalent of chocolate. Derek is hot, adorable and kind but he has no flaws. Peter has tons of flaws and it makes me hate him and love him, because on one side we know he loves Rahul and on the other side we hate him because he cheated on Rahul despite loving him.
On to Rahul/Derek-dynamic: They work great together. They're cute as hell and still feisty and they basically mimic the Peter/Rahul-dynamic minus the passion.
I love both ships, I do, but I like Peter/Rahul a smidge more than Derek/Rahul.