What would be the most plausible evenly matched alliances in a ww1 scenario?
IchBinDieKaiser
A lot would depend on the POD and more importantly perhaps, when it was. Early enough and you could have something that seems totally outlandish to us, both it terms of which powers are involved and what seems to balance. I.e. make the POD ~1850 and you could have a mega Ottoman Empire, powerful CSA, Prussia + very powerful France v Britain, US, Austria + Russia say.
If your presuming a post-1900 POD things are simplier but still a fair amount of options. The big issues would be the US and to a lesser degree Britain as both could be latecomers to the party so to speak and hence time taken to moblise their potentially massive forces.
The other uncertainties are leadership capability and luck. OTL the war was costly and very close for much of its path in part because errors my the allies meant their superior resources didn't really become decisive until later in the war.
If you want something closer than OTL but without major imbalances in the quality of the leaderships of any power from OTL levels possibly Britain, Germany, Austria, Japan, [+Turkey from early on] v France, Russia, Italy [+ US from early on]. Alliance A would have a clear advantage in Europe and probably at sea [depending on date of POD as if an early alliance with Britain Germany would probably have a markedly smaller navy]. However would have great difficult forcing the US to some sort of decision before the latter started moblising heavily so could become a hell of a slog in N America while the US allies are encouraged to continue fighting by this.
Steve