Iv'e done an unbelievable amount of testing on this, both theoretical and actual field testing. As people have said before, any class can solo through all their class missions and any class can solo any mission designated for one player. Not sure, but i'm also pretty positive every class can solo heroic 2+'s as well. Where the real (and rewarding) challenge comes in is soloing flashpoints. Yes, that means the end game, not just in between. The two flashpoints i tested like crazy were The Battle of Ilum and The False Emperor. My first tests designated whether or not one would even be able to solo the mobs in the beginning; In Normal mode, a tank could not do this in any gear ( Sith Assassin used, healer companion). However, the healer could with a mix of Ilvl 146 and 126 gear (Scoundrel, roughly 50% 126 and 50%146, his companion ranged tank at all 124 gear). In Heroic mode, NEITHER could solo the initial mobs, and i will assume this applies to all classes ( as the fights weren't even close, the tank would be down before even one mob was at half health.) However, i threw in the curveball of stealth, which will allow you to tactically pick and choose battles (a.k.a. bosses). Using this tool, both the assassin and the scoundrel could reach and defeat all the bosses on normal mode ( EXCEPTION: My assassin was NOT able to defeat Serevin. The healer companion could not heal himself and me to keep up with the damage. My scoundrel handled this fine.) On Hardmode, the Scoundrel appeared to have the distinct advantage. He could heal through tons of damage the boss was throwing out, both himself and the ranged tank companion. He could defeat Gork the Indomitable, A-14 & B-16, Jendo Krey, and Tregg by healing through the damage and moving his companion. My assassin could only defeat jendo, and that was by avoiding both his flame sweep and the missiles fired. Mathematically, The scoundrel has the unbelievable advantage. Over a 2 minute period, I calculated the total amount of damage an Assassin could absorb in 50% 146 gear 50% 126 gear( with a companion at all 126 gear) at 408,589.68. This includes ALL cooldowns, medpacs, healer healing, and skill healing, as well as mitigation and critical strike rating. In FAR inferior gear( NO implants, relics, all 126 level gear), a scoundrel could handle 422,227.84 damage per 2 minutes, NOT including medpacs. Thus, for the total idealist looking to solo the hardest possible challenges... the answer seems to lie with the scoundrel/operative classes.