Personally, the best reward system I've seen comes from my favorite MMOTCG, Pox Nora:
There are four dailies, two of which are, "Play two games with a deck that is/has [X]," then there's a, "Win a PvP Match" and "Play [an Unranked] Match." There's a moderate bonus for having completed all four.
Two, unique matches which relate to each other are given as "Daily Skirmishes", which can be challenging, but are usually just interesting. Each gives a fixed amount of in-game currency, and completing them both gives another one's worth. (Now, someone on another thread mentioned something abo