I adore Corrin/Leo for several reasons. Their S support is adorable, I like the idea of Forrest being Kana's big brother, and it actually makes perfect sense considering Corrin is implied to be Robin's past life and most of the support involves Leo giving Corrin lessons about strategy.
For couples I don't like, I don't feel comfortable pairing Elise with anyone for obvious reasons. Also I found Takumi/Oboro rather bland.