I've played with Index. It's pretty bad. For context, imagine if Ponder didn't draw you a card. Index is pretty close to that, except you can't shuffle if the cards you see are absolutely miserable. Instead, you get to see 2 more cards.
UR will probably be a better choice, since you don't have a good 2-mana Black removal spell unless we get one in RtR. RtR might change the equation, though, since come on it's no spoiler that Return to Ravnica will be a multicolor block.