Assyria- their UA allows you to beeline military techs without falling behind in other areas. Even if you don't capitalize on their UU, Assyria is still a very good warmonger because of their ability to stay at tech parity even while dumping a lot of beakers into the bottom of the tree.
Germany- their maintenance reduction applies to all land units instead of just melee, it doesn't take much math skills to figure out that the typical civ V army is going to cost less for Bismarck than it does for Shaka. The barb conversion allows you to war early while not sacrificing your early build queue. The Hanse gives you extra hammers to build more buildings and troops. Basically extra gold and hammers that can allow you to take a less focused approach allowing you to have a backup VC lined up.
Arabia- The UU is one of the best in the game. The bazaar gives you extra trade gold. The UA gives extra oil which means more late game units.
Poland- Eh, they're good at anything, period. Hammers and Sopols can translate into anything. I'd like the winged hussars better if they didn't have such a stupid long wait for an upgrade. They're awesome in the Renaissance, ok in the industrial then just a drag on your economy for almost 2 eras. Worst aspect of Poland imo, luckily their UB and UA are both awesome.
Inca- The hill movement makes logistics a lot easier, the UI is good for growth and production and the reduced tile maintenance saves money and allows you to build roads to move troops that you probably wouldn't have built otherwise
Those would be my top 5 for a balanced warmonger approach (I assume you mean being able to warmonger and do something else as well) but any civ with production or science bonuses would be good for "balanced" warmongering imo since those are the two commodities that really translate into anything. I'd say gold but I find the larger you get the smaller the impact of gold purchases and warmongering generally means you get big. Better to have extra hammers in all of your cities than the ability to gold purchase in a few of them.
As far as wrecking a continent fast goes, no one beats the Huns, no one. Rush the wheel and bronze working and go crazy. You can worry about other stuff later. By the time you meet the civs on the other continent you can say "Yeah, it was weird, I started over here all by myself. Those cities? Yep I founded them all myself. I believe in peaceful prosperity and love of my fellow man
" They do have the added benefit of a few extra hammers from the UA which does help them in other areas too.