I'm inclined to go with the alien I created for my hero team The Defeateers--Zargor, the Man from Mars.
". . .a creature with glistening green skin, two translucent blue orbs for eyes, a thin, lipless mouth, and two small holes where ears would have been on a human on either side of its hairless head. He wore a silver, form-fitting flight suit with a black metallic belt; slung over his shoulder was his BRZAP! Gun, which could fire blasts of BRZAP! Energy at any setting he needed---and as he stood beside his hovering saucer, it was obvious to even the most casual observer that this being would have to stand on highest tiptoe to see over the top of a yardstick."
His flying saucer can go from zero to escape velocity in 3.7 seconds, but has no weapons or energy shields--it's not a warship. He came to Earth to hunt down crooks for the fun of it--although when the blaster bolts start flying and the cars get tossed around like ping pong balls, he has to wonder what the bazatta he was thinking.