The Ancient Era is so interesting because it was the beginning of Tactics, Chariots and such
The Roman Era naked the dawn of conquering, instead of raiding the Romans actually assimilated the countries they invaded
The Middle Ages, the politics are interesting in this era, all the backstabbing within Europe, and the Crusades, Saladin and King Richard were the pioneers of Chivalry, when Richard was sick with fever Saladin sent him snow, an extreme luxury in Arabia. The mounted combat was also interesting, considering archers and footsoldiers were far more usefel, and yet, they held so much less standing.
The Renaissance Era is good from a tactical point of view, Horatio's naval prowess is probably still unmatched (as it is no longer necessary)
the dawn of the Gunpowder Age Sure, gunpowder was used in cannons long before, but it was the best I could come up with, Corteses assaults are impressive, fighting through unfamiliar territory with men with low morale, severely outnumbered, and yet he still retained command
The Pre WW1 Era also captivates me, the way that guns and swords worked in unison is interesting, but the Civil War was ridiculous, the two sides just marched towards each other shooting at the other side, with next to no tactics
WW1 itself was the beginning of Trench Warfare, taking the siege away from points of tactical signfigance
WW2 is by far the most interesting war by weight of content, both political and military wise, so I placed my vote hee
Post WW2 marked the end of unquestioning nationalism, there were now obvious reasons for why the wars should be fought and why they shouldn't be fought
The Current Era is by far the least 'chivalrous' with civilians becoming the main target not soldiers