My Herald Level pick- Protege, the GotG foe.
There's no fansite with a bio up that I can find, but in a thread on the Image Comics boards creator/writer Jim Valentino himself posts a synopsis and pictures of the relevant issues. I would hope that (along with scans) would be sufficiently authorative. (so to speak) If there were characters above Herald Level around, the Protege could break the power caps. Since there aren't, he's effectively capped there too. He will actually start each bout at around Enhanced Meta level.
The Super-Skrull in all his badass shape-shifting FFish brutality. Power Levels are at 60's FF scale and no booster beam. Evengel94 calls his strength at ~50tons. While he has more experience than he did in his first appearance, he's not as good at using his powers as the FF are. Use of his Hypnosis power will be severely limited limited by rules 2 and 8.
While he will be packing his usual tech-pak & weaponry, this is not the robot Techno form, which would of course be in a higher power class.
Before anybody grouses about Doom being Herald Level based on his tech prowess, keep in mind the following:
a) Fixer's tech-pak, while perhaps more versatile, is nowhere near durability the over-all power of Iron-Man or Doom's armors. Doom can get pounded on by the FF all at once, at least for a little while. IM gets back up after punches from the Hulk. Fixer could not.
b) While the Fixer may be the fastest gadget man in the MU, he's not in Reed and Doom's league in terms of sheer do-the-impossable super-science. Fixer builds cool weapons and super-gadgets, out-foxes traps, and such. Doom builds time machines and steals the Power Cosmic from the Silver Surfer. Not even close.
c) Doom personally has high-level super-powers. Even though the Ovoid mind-transfer is banned, Doom is still a powerful enough wizard to have made the finals in Aged Genghis's tourney for the mantle of Sorcerer Supreme in the Doctor Doom/Doctor Strange graphic novel.