As far as the show is concerned, I watch it for Gurmeet, Kratika, the kids, the entire support cast and of course the story, and the direction ( which occasionally goes haywire, but otherwise is top-notch)!
But if I have to choose between Gurmeet and Yash, well in that case, I love Yash because of the way Gurmeet plays him. Every action, reaction, every little smile or every tear, his happiness, sadness, pain, innocence, toughness, everything has been given form by Gurmeet...and of course the writers.
So I think we all love Yash because of two reasons :
1. We love the way Gurmeet plays Yash..its his acting which keeps us glued to Yash.
2. We love Yash because of his character, which has been written by the creatives and Shashi ji.