It really depends on the pilots and any Skills they have.
However, going from stock equal pilots, I'm going to say the Thunderbolt because Clan Tech is cheating tech.
The Awesome has more Damage at range, but the Thunderbolt can match half of it at long range, and is far more brutal at close range, and doesn't have that very vulnerable IS XL engine.
The Thunderbolt has no reason to get close, much less stay close to the Atlas, so once that LRM is out of Ammo, the Atlas can do nothing.
As for the Rifleman, only a superior pilot could handle that to a victory against either the Awesome or the Thunderbolt. Both will outgun it at range, and they already carry more Armor.