Nihilus was cool. I give him that.
But Big G is far cooler in my honest opinion.
I mean...the guy was the only survivor of the last big bang. He became Galactus and is important to the balance of the Marvel Universe. He is not really evil, but he ain't a pacifist either. He creates kickass heralds like Silver Surfer...If you destroy him you are only causing trouble to the Marvel Multiverse by releasing Abraxas...and the coolest thing is that after the Marvel Universe dies he is destined to return all the energies he collected to become the next Eternity.
Cool beyond cool. Too bad Marvel just likes to job his ass.