In this case, I had to do some soul searching. I narrowed it down to two possible couples, but one of them just barely edged out the other. In second place, we have Takasu Ryuuji and Aisaka Taiga. They are fantastic together, and Toradora is an amazing anime. That being said, there is one couple that I really liked over all the other possible couples I've seen. If it weren't for this pairing, the show that they are from would be pretty boring. In fact, I would say that I kept watching this show specifically for their interactions. That fantastic couple is
KRAFT LAWRENCE AND HOLO (SPICE AND WOLF)
These two characters, on their own, could carry a show from good to great. Paired together, however, they are so strong that a show where absolutely nothing happens (almost) is fantastic. Holo is the perfect mix of abrasive, adorable, intelligent, and perceptive. Lawrence is a great merchant, and is very dedicated to the promises he makes. Theirs is a true story of trust, and they absolutely would never, ever betray each other.
But that's not really why I love them so much. Not only are they awesome characters, but their interactions are what make them great. Holo, for instance, is full of subtlety. Everything she does has a hidden meaning behind it, but Lawrence is very quick to figure her out. This is central to the plot on many occasions. For example, the second half of the second season is based almost entirely on Lawrence making a mistake with respect to Holo. The tension created when he screws up is so enormous with respect to the rest of the anime. It's both amazing and terrifying.
You can expect this sort of stuff from Holo all the time. They never failed to leave me without an awesome scene. This should be on everyone's must-watch list.