The money may be in the ODIs, but test cricket is cricket in it's purest form, and in my opinion, far superior. I find test matches a lot more interesting. There tends to be more periods of the game where one teams on top, then the other and so on.
There is a ranking system for ODIs but it's probably easier to understand aincent Greek than the points system for that.
I've actually been working on another rankings system myself that takes into account ALL international matches. (Tests, ODIs, tour matches, ICC trophy matches and more) there'll be one based on the last 10 years, and one based on this year..... and there's some surprises in some of the individual years too! I'll be setting up a website with it on soon.