Demonic Phoenix
Problem with her acid technique is that she can only use it when none from her side are around, unless she is the type to sacrifice her own ninjas. Personally, I don't think she's the type. Also, there's the risk that the Acid technique could blow all over the field and affect her own ninjas anyway. IMO, I don't see her using the acid technique in the open, not unless she tries to release a small amount, just enough to corrode one person.
Yea, she'd have to use lava more if she had her own people around, but the possibility of using boil release when on her own is still there and capable of inflicting major casualties.
Also, she can control the acidity- after Sasuke escaped and there was a hole in the wall, she turned it down. So if the wind changes she can prevent it from hurting allies.
Tsunade would be more of a support member, as she's a medic-nin. If there are other big-players on the field, like Jiraiya, and/or Orochimaru, she wouldn't be as involved as they are when it comes to combat. She'd still take out small pockets of ninja with those crater creating punches of hers, or one-shotting each ninja, and she's also trained herself to avoid attacks. Then there's her ability to remotely heal people via Katsuyu.
Quite, though as we saw in the Hanzo fight, she was still up there alongside Orochimaru and Jiraiya fighting him.
I think her strategy depends a lot on the assets she has with her. With a small elite group, she's better off forward in the fight, while with an army she's further back, at least unless they run into a foe the normal forces can't handle without her aid.
With enough sand, he could likely take on small armies by himself. Personally, I see him starting a battle at the front, while gathering enough sand to fill a very large area, and trying to bury every enemy on the field. Some might escape or avoid, in which case, he would send in his forces to deal with the strays.
Gaara's really great strategically.
Though, lacking shukaku now, he might have less chakra and thus not leap to using sand tsunamis and such too quicky if the enemy has an S-class. They're likely to survive, and harder to deal with if he uses up chakra on uber moves.