Mark I is the one he built in the cave, he couldn't solo with that. But I still say Avengers because of him, Captain America, and Hawkeye. Hawkeye would be a big problem.
Gender: Male Location: Stuck In the future where Akus evil
Id still say the avengers without Iron Man. I feel Cap and Hawkeye would be really big problems. Then you have the rest of the back up to help draw aggro.
Let's not forget the Expendables have taken out a small army without Trench, Gunnar, Church, Booker and Billy the kid (not that he's worth that much). They're not to be underestimated. As for Iron Man, Chuck soloed a tank in EX2 and those explosive rounds Crews packed in EX1 would probably do a number on the Mark I as well. He won't be stomping anyone.
Hawkeye would probably shoot Billy with an arrow before he even had time to pull the trigger.
Cap was decimating tons of people with advanced weapons.
Black Widow was cartoony as hell when it came to fighting. I wouldn't be surprised if she managed to beat 2-3 of the Expendables in H2H combat/gunfire, or out duel Barny Ross in Handgun combat.
IM's suit in this probably won't stand up well but he will definitely be able surprise a couple of the Expendables who aren't ready for him, and those flamethrowers could give them more than something to think about.