What gives more value for money : 7 day XP boost or 10 wins?

7 days if you play more then 10 games X).

Tbh, I really wouldn't do an exp boost; once you're 30, you're done with exp which is inevitable. If you're new to the game, you really want the experience of growing slowly because it helps you learn the game more imho. You should save RP for skins.

The 7 days i mean im sure in 7 days you will win more then 10 games or so i hope.. lol

Depends on how many games you play. But 7 day XP boost should be more worth