One of my smoothest game on hydra was a Batarian/Melee Krogan combo with Cryo Falcon Asari Justicar and Drell Adept with Paladin against Reapers.
Batarian initiates with Ballistic Blade, Krogan follows up with Inferno grenade, trash is headbutted, the Batarian Falcon punch tough ones under the asari justicar bubble who is busy freezing/stunlocking marauders/cannibals trying to snipe.
The Drell detonated the justicar bubble/reave and dealt with a few ravagers from far with his Paladin, he added burst damage with cluster grenades but pretty much played like a "sniper adept" using the Justicar frozen target instead of Stasis.
We all waited for banshee to lose their "blue aura" then just meleed the crap outta them, they never lasted more than a few seconds with krogan/batarian heavy melee spam and clusternades. The few deathgrab attempts were cancelled by biotic explosions.
Game lasted 19 minutes or so.
Batarian was top, followed by the drell, the Justicar was last but her bubble and Cryo control were probably the cornerstone of our success.
Melee Batarian Soldier/Melee Krogan Soldier/Sniper Drell Adept/Falcon Justicar.
Personally, I don't care about N7 ratings, class specialization or weapons loadout. The only thing that matters is HOW you play as a part of a team to ensure objectives and team survivability.
This sums it up, if you are not confident in your randoms, just get ready to carry them: Play safe, save your consumables and use your mic, I have turned many "fail" games just by asking politely people to do X or Y, if you top-score they will rarely ignore you.