Well. Most of the ARC's were trained by Kal Skirata a very strict and hard teacher but a loving and soft one still.
The Delta boys however they were trained by Walon Vau one of the meanest mandalorians ever to set foot in the SW Universe.
ARC's have a higher genetic template but the Delta clones were trained much harder and actually had more threatening their lives due to Vau than the ARC's did. Plus Vau drilled Bloodlust into them making them a bunch of mean mother ****ers.
Secondly the Delta's work in a unit and they draw and learn from each other so Boss would have some of the knowledge that others in his unit would have unliked the ARC's who work alone. Granted its because they are good enough but they learned what they learned in training as opposed to Boss and Fixer and Scorch and Sev who continue to learn through experiences in their travels. Granted the ARC's may have some social experiences outside of themselves but ARC's work alone using recon tactics so they don't socialize and learn much more after their training at the hands of Skirata is done.
I would give Boss a equal skill to Ordo just because he keeps on learning and he knows different stuff and was trained harder than Ordo was.
Third. The Delta clones have to deal ALOT of Improvised Weaponry and Foreign weaponry plus they have the Interchangeable Weapons systems while the ARC's only have the Westar M5 and dual Pistols plus a PLX-1.
Hand to Hand its a Draw
Weapons I give it to Boss
Survival Tactics is a Tie
Physical Strength and Endurance I give to Boss (He was drilled harder)
Mental Strength and Knowledge - Ordo
The only drawl back for Boss would be that he doesen't have that rogue lets go get them at all costs type personality.