My answer is NONE. There is no "best combo" with scout. At least not with a single card.
Scout needs to combo with no less than 3 other cards on the board to be even worth acquiring. This is the problem with scout.
There are players who will tell you that you should never buy scout. They are wrong.
But the occasions where buying scout is actually a good idea is rare, and even then, the scout is a secondary part of strategy, often to be added later into the mix