SCMMs include, Mohawk, no contest. That's been my favorite Mech since it entered the game and the only one that beat out the HammerHead. Loki comes in second. I love the Lo0ki's look and it's fun to use.
Mohawk though...everything about it is so perfect! Head design is sweet, it looks like a war machine, and the leg design is really unique. I'm disappointed it will be left behind due to cap things actually, but that's the way the game works.
The HammerHead is another great one. Art is fantastic. Only issue...for some reason the scaling is incredibly strange. The Mech's height should be somewhere around the Advanced WolfBlade's given how the weapons appear on it. As a result it looks obscenely tiny.
Drakel Power Armor/Corrupted Drakel Power Armor looks incredibly smooth and Alien which I love. Shame other Planets haven't had a signature "look" for their Mechs that worked as amazingly.