Honestly, I would go with the one who has the best, most pronounced lacing. I personally like the med blues, which allows for the hackle and saddle feathers to be in nice contrast to the body color. Depends on how dark or how light your boys are, too, I would think. Do you have pictures?
I neglected to mention the body type, sorry. Maybe your smaller rooster is just a slower-to-develop one. Orpingtons can take awhile to fully fill out. Body type is most important than color, however, if your only final issue is color, I'd go with better lacing. If that better lacing is on a puny, narrow body, then I'd go with a better body. Hope that makes sense.
I personally like your Splash and the dark cockeral, he has nice lacing....It takes months for cockerals to show their true colors and I mean months....
I would wait another another couple of months before even trying to decide which one to keep. They change alot when they start looking like a more mature rooster.
I like the dark lacing and you can never judge a splash that young.
Please wait. You may be kicking yourself in 6 months for a hurried choice.