I'd like to see the percentage of winning of my deck (and the number of games played with this unchanged deck) and the percentage of the same of the opponent's deck I'm playing with. I.e. Deck #1: winning percentage 6/10 (60%). Or something like that.
Just to make it properly it should NOT be a personal stat, like the percentage of YOU as a person winning, because it would discourage experimenting with different decks. It should be you playing a certain DECK (if you keep this deck saved it should have the stats available, if you delete the deck or change it then stat should either disappear (deleted) or reset (changed)).
The stat should also help you understand how your new is performing in comparison to your previous deck.