Which battle throughout Tamriel's history do you think was the most significant?
Which do you think was the most interesting?

I read the book about the Battle of Sancre Tor, and was displeased with it. It says historians 'marvel' at Talos, and acts as if it is such a big important battle in Talo's life, but I saw nothing significant about it. He lured the Nord-Breton alliance out of the castle, snuck in, and took control of it. Quite personally, I don't see why this is such a big feat.

Most significant? I like to think the Battle at Red Mountain is pretty high up there.

Red Mountain is definitely up there. The Sack of the Imperial City during the Great War is probably somewhere up there, as well.

I'd say the battles of the Alessian revolution are both the most interesting, and most significant. They radically changed the power structure in Tamriel, and they featured The Whitestrake goin' around wreckin' [censored]. Those were the times, man. Those were the times.

Battle of Rimmen, which caused the Middle Dawn and scattered the Numidium.

Red Mountain, which created Numidium and the Tribunal and the Way of the Voice.

Possibly that time when King Lysandus was killed, which led to the plot of Daggerfall, which then gets involved with Numidium.

Any other battle involving Big Stompy Robot.

Also:

The Alessian Revolution, involving Little Stompy Robot.

Basically anything that involves Stompy Robots.

Battle of Red Mountain, during the war of the First Council
The decisive battles for Alessia in her war against those damnable elves (But I don't know what they are)
Tiber his big stompy robot battle in Summerset
The Imperial Legion under Martin Septim fighting for control over the Imperial City which saw the eventual defeat of Mehrunes Dagon

and

The battle Vivec lost in the end of 2920, which caused the truce. Which I believe is the only reason anybody dared assassinate the Reman line of Emperors, so effectively it was in my opinion the catelyst for the fall of the second Empire

What about that one where half of Tamriel united to sink Thras?

I'd imagine that's less significant in the battle itself, and more so in the fact that all of Tamriel united of their own free will.

The battle of Glenumbria Moors seems to stick out for me. It ultimately destroyed both the Direnni Hegemony and the Alessian Order and gave rise to King Wulfharth (who took the throne of Skyrim after Hoag's death at Glenumbria)

Another one: pale pass

The Battle of the Red Ring, and Battle of Red Mountain.

The battle that occured in the Imperial City during the Oblivion Crisis. It lead to the end of the Septim Empire, the rise of the Aldmeri Dominion(Thalmor claiming credit) the decline of Talos worship, as well as stopping Mehrunes Dagon claiming dominion over all of Tamriel. There are plenty of other things as well but thats good for now i think.

Disaster at Ionith anyone? ended all hopes of an Imperial expansion into Akivir with a high price of Imperial loss's as well as the death of an Emperor.

The fall of the Snow Elf Prince.

I wish the battle for Bruma had been more epic. There ought to have been scores more NPC's than the unmodded game provided.

Stompy robots are good, i like stompy robots!

The Battle of Firewaves, of course - where the Camoran Usurper was defeated. Else we'd all be skeletons, hurrrraaaay.

Which Battle?
When Galerion led an army of Nords against Mannimarco, and recieved no assistance from the Mages Guild?
When the Akavirri surrendered to Cyrod after getting Shouted at?

The battle where Cameron Usurper was defeated by combined naval forces, said to have been so great that it would take many books to cover all of it. Also, the battle for the Imperial City during 3E 433, I mean c'mon a Daedric Prince invaded!