Here is what the strategy guide says so if you don't wanna know don't read this comment. If Collector Base was saved:

If your readiness ratting is below 1,750 points, Earth is destroyed regardless of the choice to destroy the Reapers or become one.
1,750 rating, if you choose to destroy the Reapers, Earth is destroyed.
2,050 rating, if you choose to become a reaper, Earth is saved.
2,350 rating, if you choose to destroy the reapers Earth is devastated but still there.
2, 650 rating, if you choose to destroy the reapers, earth is saved.
2,800 rating, you're able to create synergy between organics and synthetics, saving earth and the galaxy..
4,000 rating, if you choose to destroy the reapers and "saved" Anderson, shepard Lives
5,000 rating, if you choose to destroy the reapers and did not "save" Anderson, Shepard Lives
If the collector base was destroyed.

Below 1,750 rating, earth is destroyed regardless of what you choose.
1,750 rating, if you choose to become a reaper, earth is destroyed.
1,900 rating, if you choose to destroy the reapers earth is devastated but still there.
2,350 rating, if you choose to become a reaper earth is saved.
2,650 rating, if you choose to destroy the reapers, earth is saved.
2,800 rating,you are able to create synergy between organics and synthetics, saving earth and the galaxy.
4,000 rating, if you choose to destroy the reapers and "saved" Anderson, Shepard lives.
5,000 rating, if you choose to destroy the reapers and did not "save" Anderson, Shepard lives.
There is a special rewward available only to players who have imported a save from ME2 with the Prejek Paddle Fish purhased by Commander Shepard. If the Prjeck Paddle Fish survives through all of ME3 and ME3 New Game Plus, visit Liara's quarters aboard the Normandy for a very special intel bonus.**