In terms of just 1st party Sony characters, I'd like to see any of the following:
Kutaro (Puppeteer) Gabe Logan (Syphon Filter) Robbit (Jumping Flash!) Joel (The Last of Us) Dart (Legend of Dragoon) Ico (Ico) Knack (Knack) Wander (Shadow of the Colossus) Iota (Tearaway) Captain Blasto (Blasto) Rudy Roughnight (Wild Arms) Nathan Hale (Resistance) Lammy (Um Jammer Lammy)
And there are more, but the list was getting too long anyways.
Crash vs Spyro Rayman vs Croc Tomba vs Klonoa Cloud Strife(Final Fantasy) vs Dart Feld(Legend of Dragoon) Abe(Oddworld) vs Blasto Parappa vs Spike Heihachi(Tekken) vs Toro Sir Daniel(MediEvil) vs Raziel(Legacy of Kain) Sweet Tooth(Twisted Metal) vs Scorpion(Mortal Kombat) Solid Snake(Metal Gear) vs Gabriel Logan(Syphon Filter) Jak vs Ratchet Sly Cooper vs Gex Rau Utu(Mark of Kri) vs Monkey(Enslaved) Raiden(Metal Gear) vs Dante(Devil May Cry) Wander(Shadow of the Colossus) vs Toan(Dark Cloud) Nightmare(Soul Calibur) vs Nemesis(Resident Evil) Jade(Beyond Good & Evil) vs Jennifer Tate(Primal) Kratos(God of War) vs Nariko(Heavenly Sword) Nathan Drake(Uncharted) vs Lara Croft(Tomb Raider) Colonel Radec(Killzone) vs Chimera Hybrid(Resistance) Sackboy(Little Big Planet) vs Kutaro(Puppeteer) Cole McGrath(Infamous) vs Alex Mercer(Prototype) Kat(Gravity Rush) vs Emmett Graves(Starhawk) Main character from Soul Sacrifice vs Ellen(Folklore) Edward Kenway(Assassins's Creed) vs Ryu Hayabusa(Ninja Gaiden)
The perfect roster imo. The sequel could have 40 characters initially, but could get 10 more characters through dlc. This could easily be done if the sequel is in the hands of an experience development team.