Wonder Man got his powers from Baron Zemo. He's a ionic being. WM and WW are compartively equal in strength. But Diana has the edge in superspeed, warrior know-how, and her unbreakable silver gauntlets. Go to wizardworld.com (I don't know if its still up) and you'll see that Diana won by plunging her crossed fists into his ionic body and disrupted due to the forcefield generated by her gauntlets that distills any and all energies. (That's why she can reflect everything)
First of all, usually Diana doesn't use silver gauntlets, the only weapons she use are the wristbands and the lazo.
Second, Wonder Man possess superhuman reflexes and speed too, his flying speeds are mach speeds, equal to those that the Quinjet or Thor can reach.Also Simon possess battle experience too, he goes head to head with Thor, also Hulk, he fought against many enemies with the Avengers, yes not the experience of WW but sufficient to show his own.
I think that Simon can win only if he's actually able to shot ionic energy blast, that would grant him a great advantage.
K3VIL by silver gauntlets, I meant silver bracelets. Silver gauntlets sound cooler anyway. Wonder Man is very strong but hes not a warrior like Diana. His fighting skills are average at best. He's relied on his strength and invulnerability to win his battles. WW's been trained to be a bloodthirsty killer since the day she's been born. See the reason stated above in my previous thread