Rainbow Dash x Will- These two are more of the "opposites attract" type which I can see that, Dash being the athletic stubborn Rolemodel while Will is the cunning responsible Merchant, these two are so different yet so similar. And both don't have to change each other/themselves for the other, Will can still travel around Equestria and Rainbow Dash can try to be a Wonderbolt or whatever she wants to do with her life. And they don't have to feel alone because Dash can easily use her speed to fly around Equestria and easily find Will on his travels and give him a big ol surprise hug. Not sure if they'll have any problems though, kind of a mystery.