Hi everyone,
I was reading all of the Handbook HC pages and I realized that there were no more than characters on the cover. And all of them were popular. Here's my proof:

Volume 1: Abomination, AIM, Angel, Annihilus, Apocalypse, Ares, Atlas, Aurora, Banshee, Beast, Bishop, Black Bolt, Black Cat, Black Panther, Black Widow (15 characters)

Volume 2: Blade, Blink, Brood, Bullseye, Cable, Luke Cage, Cannonball, Captain America, Captain Britain, Captain Marvel, Carnage, Citizen V, Clea, Cloak, Colossus (15 characters)

Volume 3: Crossbones, Cyclops, Dagger, Daredevil, Darkhawk, Dazzler, Deadpool, Karolina Dean, Doc Samson, Doctor Doom, Doctor Octopus, Doctor Strange, Doop, Drax, Electro (15 characters)

Volume 4: Enchantress, Eternity, Falcon, Fin Fang Foom, Firestar, Fixer, Forge, Frog-Man, Emma Frost, Nick Fury, Galactus, Gambit, Ghost Rider, Grim Reaper, Guardian (15 characters)

Volume 5: Havok, Hellcat, Hellstorm, Hercules, Hobgoblin, Howard the Duck, Hulk, Human Torch, Hydra, Hyperion, Iceman, Ikaris, Invisible Woman, Iron Fist, Iron Man (15 characters)

Volume 6: Jonah Jameson, Juggernaut, Kang, Ka-Zar, Dan Ketch, Kid Colt, Killraven, Kingpin, Klaw, Living Tribunal, Lockheed, Loki, Longshot, Machine Man, Madame Masque (15 characters)

Volume 7: Magik, Magneto, Man-Thing, Mandarin, Marvel Boy (Grayson), Marvel Boy (Noh-Varr), Marvel Zombies, Medusa, Meggan, Mephisto, Mikaboshi (who obviously took Mister Fantastic's place), Mister Sinister, Moon Knight, Moonstone, Ms. Marvel (15 characters)

Volume 8: Mysterio, Mystique, Namor, Namora, Night Thrasher, Nightcrawler, Nighthawk, Northstar, Nova, Odin, Onslaught, Norman Osborn, May Parker, Patriot (Bradley), Phoenix (15 characters)

Volume 9: Polaris, Professor X, Kitty Pryde, Psylocke, Punisher, Quasar (Phyla), Quicksilver, Radioactive Man, Red Skull, Rhino, Franklin Richards, Rocket Raccoon, Rogue, Ronan the Accuser, Ronin (15 characters)

Together we have:

Abomination, AIM, Angel, Annihilus, Apocalypse, Ares, Atlas, Aurora, Banshee, Beast, Bishop, Black Bolt, Black Cat, Black Panther, Black Widow, Blade, Blink Brood, Bullseye, Cable, Luke Cage, Cannonball, Captain America, Captain Britain, Captain Marvel, Carnage, Citizen V, Clea, Cloak, Colossus, Crossbones, Cyclops, Dagger, Daredevil, Darkhawk, Dazzler, Deadpool, Karolina Dean, Doc Samson, Doctor Doom, Doctor Octopus, Doctor Strange, Doop, Drax, Electro, Enchantress, Eternity, Falcon, Fin Fang Foom, Firestar, Fixer, Forge, Frog-Man, Emma Frost, Nick Fury, Galactus, Gambit, Ghost Rider, Grim Reaper, Guardian, Havok, Hellcat, Hellstorm, Hercules, Hobgoblin, Howard the Duck, Hulk, Human Torch, Hydra, Hyperion, Iceman, Ikaris, Invisible Woman, Iron Fist, Iron Man, Jonah Jameson, Juggernaut, Kang, Ka-Zar, Dan Ketch, Kid Colt, Killraven, Kingpin, Klaw, Living Tribunal, Lockheed, Loki, Longshot, Machine Man, Madame Masque, Magik, Magneto, Man-Thing, Mandarin, Marvel Boy (Grayson), Marvel Boy (Noh-Varr), Marvel Zombies, Medusa, Meggan, Mephisto, Mikaboshi, Mister Sinister, Moon Knight, Moonstone, Ms. Marvel, Mysterio, Mystique, Namor, Namora, Night Thrasher, Nightcrawler, Nighthawk, Northstar, Nova, Odin, Onslaught, Norman Osborn, May Parker, Patriot (Bradley), Phoenix, Polaris, Professor X, Kitty Pryde, Psylocke, Punisher, Quasar (Phyla), Quicksilver, Radioactive Man, Red Skull, Rhino, Franklin Richards, Rocket Raccoon, Rogue, Ronan the Accuser, Ronin (135 characters)

And with the other three handbooks, there will be 180 characters on all twelve covers. Here are my bets for the last three covers:

10: Sabretooth, Sandman, Sasquatch, Scarlet Witch, Scorpion, Sersi, Shang Chi, She-Hulk, Silver Surfer, Skrull, Songbird, Spider-Man, Spider-Woman, Stature, Storm

11: Strong Guy, Sunfire, Super-Skrull, Supreme Intelligence, Taskmaster, Thanos, Thing, Thor, Thundra, Tiger Shark, Tigra, Toad, Uatu the Watcher, Ultron, USAgent

12: Valkyrie, Venom, Viper, Vision, Vulture, Wasp, Mary Jane Watson, Wizard, Wolfsbane, Wolverine, Wonder Man, X-Man, Yellowjacket, Zombie, Zzzax

Hope you like it. Amen.