From what I can tell the Thalmor have been very aggressive and have manipulated history to their means by to even that they personally stopped the oblivion crisis. They are extremist and believe in racial superiority and have been weakened by the Great war just not as much as the Empire.
The empire From what I can tell they have a more liberalism point of view favoring diplomacy or war. The original empire died with Martin Septim. They have played important roles in history and was created by Talos ( historical version of modern day Ulfric Stormcloak (check out the simalirities) ).They were decimated by the war with the Dominion and left weakened even more so by the now inevitable independent Skyirm.
The An-xileel. They are a political party that does not manipulate history. They not only held off the invading Deadra in the Oblivion crisis but actually invaded Oblivion itself. With help from the hist recalling every Argonian to black marsh. The An-Xileel was the reason why Black March separated from the Empire but also they rallied the Argonians enough so that they could defeated the Deadra. They conquered (for the most) part Morrowind but have flown underneath the radar on current events and most people do not know who they are.
The An-Xileel as I see it are the most long term threat. No one has ever won a war with the Argonians and it is next to impossible due to the rough terrain of Black March. They have conquered Morrowind and have sent the Dunmer crying all the way to Solsteim. I fear that the Empire and The Thalmor will exaust Tamriels defenses enough for the An-Xileel to march across Tamriel without much of a fight.
The Thalmor The Empire and The An-Xileel along with Hammerfel is probably how I would like . 4 great empires battling it out here and there.
So what do you think is the best hope for Tamriel
Empire , Thalmor , or An-Xileel?

I'd say the Empire, from what little I know; mostly because they seem far more moderate and diplomatic then the other two, who seem pretty extreme (especially the Thalmor); of course, as I said before, I'm certainly no expert in the subject.

as a an xileel supporter id say they dont really want war but i cant imagine theyd wanna be ruled by elves again so they will problly join the independant provinces or a united empire

The An-Xileel.

The An-Xileel.

Thalmor. The High Elves have a naturally defensible position in Summerset, and even Tiber Septim wasn't able to force them into the empire until he used the Numidium. The Empire as a close second, or more likely an on going bloody stale-mate/cold war between the Aldmeri and the Empire. The An-Xileel last, they may be powerful but the argonians have no natural allies and are widely discriminated against as beastfolf, an attack on all fronts would probably push every one against them. Finally no one conquered black marsh because a) the cost of taking and holding the territory wasn't worth the benefit of it and b ) not even the dunmer hate the lizards enough to go and burn the place down in a genocidal rampage.

The An-Xixeel are pathethic opportunists.

It's not a question of who is the best, its a question of who you favor.

None, I'm against imperialistic governments, they tend to become corrupt far before they reach their height and in the case with those three, they are all rotten to the core. It's like asking me to choose a turd from 3 different animals.

Thalmor. I like their attitude and they know how to get things done.

I have to say the Empire.