Okay, I'm a Krieg fangirl, so… Gotta vote for him on this one.
First off, someone said several posts ago that Krieg would lose because he's slow. Yeah... I really don't see where that came from. He moves pretty damn fast while holding a ONE TON spear with ONE hand, I'd imagine he'd be uber fast when he wasn't holding the thing.
Secondly, Krieg got defeated by Luffy, sure, but were it not for the fact that Sanji saved Luffy from drowning, Krieg certainly would have succeeded in taking him down with him. He got Gomu Gomu No BAZOOKA'D, and still had sense and strength enough to launch yet another attack. Then he got himself sledgehammered into the deck, and STILL had enough strength to (unconsciously) fend off his own crew. Until Gin came along...
We also musn't forget that his fleet only turned back from the Grand Line because they encountered the strongest swordsmen in the world.
Now then... I must admit Usopp/Sogeking had gotten LOADS stronger throughout his travels in the Grand Line. However, the impression I got from Gin's final speech was that both he and Krieg were heading back into the Grand Line also. I can only imagine that Krieg's come up against some pretty powerful stuff throughout his travels there, thus getting stronger.
Plus he has all his fancy armor, weapons, and gadgets. Sogeking just has the weapons and gadgets. Krieg's a pretty damn big guy too, whereas Usopp... not so much.
I don't think that Sogeking is physically strong enough to use a Reject Dial, and I don't think that regular Impact Dials are powerful enough to break through Krieg's armor. As stated, Sogeking has no armor, and after seeing the damage Krieg's array of guns, projectiles, and other such long range objects did to Luffy and the Baratie... I almost pity Usopp.
Although he's gotten stronger, Sogeking still gets scared and runs if he doesn't really have to fight. Krieg was extremely confident (call it cocky if you must) from the beginning.
So... If you ask me, Krieg has the means, the physical attributes, and the attitude needed to beat Sogeking.
End Don Krieg fangirling session... for now.