Alien: Dhargo from Farscape. (Since we're reaching here)
Time Matrix morph: Ever watch The Future is Wild? Pretty much any animal in our planet's future, long after humanity is gone since there will be no record of it in the present.
Present Day Earth: If I had to choose one of the cats, I would go with a Liger or a Tigon. They're stronger than either a lion or a tiger and the largest cat on Earth. I mean, just an adolescent liger is ten feet tall and grows up to twelve feet in length. That's half the size of a school bus and the a few feet higher than the tallest man on Earth.
But as I'm a sucker for non-conformity, I'm going to have to stick with my Komodo Dragon morph.