Rhino actually loses to people he should lose to most of the time though. Sure he has his shitty showings but when he's one of Hulk's rogues...
Flash loses to people he shouldn't lose to. Or he just looks terrible.
Manhunter and Rulk are about portrayed right. They lose to people they should and they beat people they should. Sure there's some out there showings but on average it's fairly OK. The issue with Manhunter though is he doesn't even know what his powers are most of the time. And shitty durability. Even if MM should lose, he makes it seem that much easier to murder him.
So with that said, Rhino wins.
For the Gamma Father, the Gamma Bomb, and The Green Door
When it comes down to it I rarely take showings of high end characters from team books. Every high end character in a team book has to job to make a team story viable. Lets face it if Superman, Thor, Alan Scot etc all operated at their best what would Black Canary, Black Widow or Wildcat ever do. Almost every single threat that the JSA has ever faced could and should have been able to be handled solo by three or four of its membership (Alan, Fate, J Thunder). Same for JLA, Avengers, Defenders, LoSH. The only teams where the team is viable without jobbing characters are where members are in a relatively even playing field or bringing something completely different to the table (FF, Doom Patrol, X-Men, etc)
when has the Flash EVER lost to Digger Harkness? The best Digger ever did was threaten inocents to divert Flash.
If we're talking his son Owen Mercer, that's a different story. Owen is a speedster too, since his mom is from the Thawne line (as in Zoom). He only has speed bursts but they are in conjunction with his throwing of boomerangs.
A boomerang that moves at speeds close to the speedster who fights the wielder of it has every reason to trouble said speedster.