The Kaiserreich hands down. I'll paraphrase Dan Carlin, the Kaiserreich was a heavyweight boxer able to keep standing for the entire bout giving and taking punches before finally going down. The Nazi Reich was a flashy one punch knockout artist and as soon as they ran into someone who could take a few punches they started to crumble.
Well said.
I think that in terms of overall military quality and basic decency compared to contemporaries, WW1 germany wins hands down. More functional and stronger economy, objectively superior human rights record, the best army in Europe at the start of the war, and despite the Ottomans' deep problems and Austria-Hungary's criminally incompetent leadership, they were still far better allies than Italy in WW2 (and the wonderful idiocy of Luigi "God's gift to the enemy" Cadorna.
Nazi Germany got the benefit of MASSIVE strokes of luck--a unique degree of Soviet officer corps weakness AND France politically paralyzed, which allowed the lightning strike into France to succeed--and they still lost due to critical failures at every level of their economy, military, and society.
WW1 Germany made a couple of diplomatic flops that left America soft-backing the Entente and not bothering to run the blockade, and even then still damn near won.
To put it another way: Nazi Germany was basically doomed either way, and their best-case scenario is economic devastation following an attempt to white-peace the WAllies after "defeating" the USSR. WW1 Germany
would have won if America hadn't intervened in '17, because by that point the Entente's collateral was gone, America was done offering loans and discounts, and French morale was in free fall.
Nazi Germany was very, very lucky. The Kaiserreich was very good at fighting wars.