Personally, I like Solar Beam because it is such a hammer. My fighting style is to wait for the defender charge move before launching mine, why I prefer Solar Beam.
But I can easily make a case for Seed Bomb as a charge move one can use more often, and it got a nice buff in the latest update.
It's the age-old debate about 1-bar charge moves vs. 2 or 3-bar charge moves. Both Seed Bomb and Solar Beam are great. I have a Bullet Seed and Solar Beam Exeggutor and I love it.
