It's probably very close, but I personally wouldn't trade Duffy for Archer right now. They are close in many regards, but Duffy currently has the edge in: age, velo, SwStr%, K/BB, ERA by a wide margin, FIP by a good margin, WHIP, OPP avg, HR rate, WAR, WAR/IP, among others. Archer has a slight edge in Ks, GB rate (not necessarily a good thing) and xFIP (with xFIP doing some serious regression to his HR/FB rate). They have identical career ERAs, but Duffy is having a much better season this year, which is what matters the most. Any argument for Archer is largely based on 2015. If you've watched Duffy pitch, there's nothing bogus about his game. He has serious heat, he's a lefty, he has a killer changeup, and he's drastically improved his command. He has everything you want to see in a legit breakout. If you just posted his numbers without a name attached, you'd probably guess they belonged to Chris Sale, except he's actually been better than Sale across the board. And Sale, like Archer and Duffy, is also 27. Duffy also has the least mileage on his arm of the three, FWIW.