My list would be this.
1/2. Batman or Captain America takes the number one slot. They can both be very lethal with the majority of weapons provided, are tactical genius's, and outclass most of the other fighters skill wise and physically.
2. I would say Punisher. As with above, he will be deadly with any of the firearms he gets his hands on. But what puts him high in the list is his survivalist training and ingenuity.
3. Snake-Eyes. He has extensive knowledge of the weaponry here, and has the skill and physicals to put down tributes in combat.
4. Wolverine. Enhanced physicals, extensive training, and adamantium coated bones.
Bucky, Ollie and Hawkeye in no particular order.