Nick and Jess (New Girl)
It wouldn't make sense for New Girl not to invest in the slow build up that they created between Nick and Jess as roommates. It was clear that these two would explore something more someday, it was only a matter of perfect timing which the show managed to deliver.
Rick and Michonne (The Walking Dead)
The Walking Dead only got better when Rick and Michonne got their love story told. There is no one who could possibly look at these two and not love their chemistry.
Fitz and Simmons (Agents of S.H.I.E.L.D.)
The wait was well worth it, and these two lived happily ever after. We refuse to hear anything else because after waiting for Fitz and Simmons to finally get together, and for it to be exactly as epic as expected, there is no other future for these two in our minds.
Emma and Hook (Once Upon a Time)
Emma and Hook's relationship had the perfect amount of waiting before the show finally got them together. There was that buildup that added to their story, without wasting too much time trying to raise the stakes before actually committing to a couple.
Ted and Alexis (Schitt's Creek)
Ted and Alexis may not have been the longest slowburn, especially since they started dating during Schitt's Creek Season 1. But in a way, it was the second time around when Alexis and Ted were the new versions of themselves that proved they were ready to have a long lasting relationship.
Holly and Vince (What I Like About You)
This is a real throwback and yet here we are because Holly and Vince were such a quality ship. It took a while for them to find their way to one another, a few boyfriends and a Thanksgiving hookup slowing them down a bit, but when they did it was clear they were endgame. Vince and Holly dating became the highlight of the show, the way they kept the bickering from their friendshp and added romance was the perfect example of a healthy relationship.