Choose your Poison (MASSIVE ENDGAME SPOILERS):
EMS < 1750: Earth is destroyed, Shepard dies, no matter what else.
Collector Base from ME 2 Destroyed (this is Default setting for ME 3,btw):
EMS >= 1750, chose Become Reaper: Earth is Destroyed, Shepard Dies.
EMS >= 1900, Choose Destroy: Earth is Devastated but still around, Shepard Dies.
EMS >= 2350, Choose Become Reaper: Earth Saved, Shepard "Dies".
EMS >= 2650, Choose Destroy: Earth Saved, Shepard Dies.
EMS >= 2800, Choose Merge:Synergy created between Synthetics & Organics, Earth and Galaxy saved, Shepard dies.
EMS >= 4000, Anderson Saved, Choose Destroy: Earth saved, Shepard LIVES.
EMS >= 5000, Choose Destroy: Earth Saved, Sheaprd LIVES.
Collector Base from ME 2 Saved (import only):
EMS >= 1750, Choose Destroy: Earth is Destroyed, Shepard Dies.
EMS >= 2050, Become Reaper: Earth is saved, Shepard "dies"
EMS >= 2350, Choose Destroy: Earth Devastated but still around, Shepard Dies.
EMS >= 2650, Choose Destroy: Earth Saved, Shepard Dies.
EMS >= 2800, Choose Merge: Synergy created between Organics and Synthetics, Earth & Galaxy saved, Shepard dies.
EMS >= 4000, Choose Destroy, Anderson Saved: Earth Saved, Shepard LIVES.
EMS >= 5000, Choose Destroy: Earth Saved, Shepard LIVES
EMS = Effective Military Strength, the 3rd line on War Assets list.
Note: Shepard gets a victory with Heroic Sacrifice if the "Paragon" choice of Destroying the Reapers is taken after gaining enough War Assets to total 5300 (easily reached by thourogh completionists) or a combined Readiness Rating (from both SP & MP) of 2650. What is so wrong with that? Dying so that others may live has always been noble....