Sadly, though I love Charr dearly, it is clear to me that the Asura would win.
Charr couldn't risk using waypoints or gates, indeed one of their first priorities would have to be to dismantle all the Asuran transport devices they could find. The Asura on the other hand can use their own technology with impunity, thus being able to hit the Charr on pretty much any front they choose ... difficult to mount a decent defence when you don't know which direction your enemy will be coming from. By the same token, any Charr attack on Rata Sum will be relatively predictable because they simply aren't mobile enough to circle round the Maguuma jungle.
The Asura have force fields, the Charr have armour. Just in terms of resources alone the Asura have the edge because their ability to defend a large surface area is limited only by the amount of magical energy they have access to (this is an unknown quantity but looking at the city of Rata Sum, they have access to quite a lot) whereas the Charr would actually have to build their armour. Granted the Black Citadel is already pretty well fortified but I think that Asuran field magitech is likely to win out over plate steel.
Adaptability and Predictability
Charr are fairly predictable in their approaches to war, they're very good with those approaches but it pretty much boils down to throwing sufficient munitions at a thing to break it. Asura on the other hand have a ridiculous array (6 completely different weapons for every 5 individuals wasn't it?) of approaches, many of which will doubtless fail but many of which will succeed. Because of Charr unity, the Asura will only have to come up with a limited number of defensive strategies ... they will have thousands; whereas because of Asuran diversity the Charr will have to come up with eighteen different defences for every single assault.
Golems sir ... Faasands of 'em
Charr infantry is Charr, Asuran infantry is golems. While golems aren't indestructible by any means (unless you count one-offs like Sandy) they're still going to prove a significant challenge, given that the Asura can use their superior mobility (see above) to dictate where any battle takes place so the Charr won't be able to bring their numerical superiority to bear.
Steamtech vs. Magitech
While the Asura don't understand how Charr technology works at the moment (based on a conversation overheard in Rata Sum) chances are that they'd be able to reverse-engineer it without too much trouble. If the Charr were to capture an Asuran device however, they would find it much harder to reverse engineer because, well, there's nothing to engineer. Asuran technology appears to be pretty much solid-state, so figuring out what it does and replicating that will be a much harder task than doing the same with a Charr device. After all, when faced with (say) the Enigma Device and a pocket calculator, I reckon the former would be easier to replicate than the latter assuming you weren't at all familiar with either technology.
So yeah, the Asura would win, and a Charr without an Asuran control collar would be a rare sight indeed.
I vote Charr victory.Superior Organization
The Charr command structure is based on that of the Ancient Romans, widely regarded to be among the best organized in the ancient world. They're organized down to a single soldier. Every Charr is trained to fight from birth, trained to respect authority, trained to put the warband first, trained to follow orders. The Charr army, on the march, is impossibly efficient and very effective. No matter if the Asura can get there faster, you can bet every Charr is going to be right where they're needed. The Asura, meanwhile, squabble about literally everything. If an Asura wants to suceed, he does it by being better than everyone else. That sort of thing does not make for an efficient military. Hell, the ones who govern the Asura do so not by virtue of merit, but by virtue of being in the wrong place at the wrong time. I would make a Sparta/Athens comparison, but I've already made one historical allusion in this paragraph and I don't want to seem pretentious.Superior Preparation
The Asura have the potential to have these defences, but they don't have them. The Asura aren't ready for a war. Snaff mentions in Edge of Destiny that they aren't prepared for an attack - all they have is peacekeeper golems and those are just to deal with petty criminals. And, if it came down to it, how many golems and forcefields and weapons could the Asura whip up in a hurry, with all their oft-touted organizational problems? No matter how industrious they are, I doubt it'd be enough to stop the Charr - who could probably get a massive army on the road in a single day.Superior Ability
Charr fight. It's what they do, what they're trained to do, what they're built to do, what they're born to do. Lock a Charr in a room with an Asura and it's pretty obvious who comes out of that room alive (and no I'm not considering badass adventurer Asura in that equation - they're anomalies and the Charr have em too). Not only that, but Charr dedicate their national existence to fighting; improving their skills, their tech, and their tactics. War is what the Charr do best. It's not something the Asura really do. I could be mistaken, but I believe they haven't gone to this sort of war in... ever. The closest thing is their relationship with the Skritt, and if I may quote Doctor Who, that is not war, it is pest control. They can't be rife with expert soldiers and military geniuses - I don't care how smart you are, you only learn the best tactics by learning from the past. The Asura have no military history of their own to go by, and would they really be willing to study the tactics of an 'inferior' race?Actual Soldiers, sir... Milluns of em':
For starters, there are not thousands of military golems - most golems are the property of the one who invented them, and that causes a whole slew of problems with the idea of each genius controls their own work and so forth so it'd probably be really, really hard to mass produce them in a hurry. Assuming the Asura could organize themselves enough to mass produce golems in a hurry and that each krewe wouldn't keep doing its own thing and or trying to win the war on their own to go down in history as the genius who conquered the Charr. The Charr, meanwhile, are an army. They have soldiers and weapons and siege equipment etc. out the wazoo. They could get an invasion going before the Asura have put together a hundred golems and finished arguing over who gets the credit.The Technology Thing
Alright, I'll concede that you've got me beat there. Asura technology is more advanced. The problem is that it's not militarized enough, there isn't enough of it, and that they probably couldn't whip up more in a hurry,
So ultimately, in open, total war, Charr win hands down.The Asura's only real chance is to flex their economic muscles, and even that may not work, considering the Charr war machine is largely self-sufficient.