70% of my ships have almost similar personalities (Stefan/Elena, Sheldon/Amy, Ana/Will, Charming/Snow, Cyrus/Alice, etc).

I guess; however, think it's less that I like both couples with similar personalities and couples with opposite personalities, but more that I don't really care about whether the couples have similar or different personalities, so long as they are compatible and understand one another and can read each other well. You don't need to have similar personalities or opposite personalities to be compatible, imo, so I've loved couples who individually are quite similar and couples who individually are quite different, and yet, they've all been equally supportive and completely understood one another.

^^ what -firemaiden- said. They just need chemistry & to fit well together.

^Agreed with above.
So, yeah both but I'm perhaps more partial to couples having similar personalities.