The Klingons, Protoss, and Jaffa at Pandora

[sonofccn]

If a 35m alkesh whose anti-ship weapons are staff cannons capable of blowing up buildings is a tough opponent for a cloaking 110m antimatter-powered warship with a duranium hull, SG is a lot stronger than I think it is and ST a lot weaker.

Well we know from Exodus (stargate season 4) that an alkesh is capable of inflicting moderate damage to a Hat'ak which isn't a small or weak powered ship. I'll see if I can dig up the clip of the episode in question but that will have to wait until later I'm afraid. A bird-of-prey isn't exactly the most powerful or heavily armored vessel in the Klingon navy and Stargate would have to be drastically weaker for an alkesh not to be any threat what so ever.

[Khas]

In a fair fight, a Navi would beat a Klingon hand to hand (and in the Pandoran jungle, a Navi with a bow will probably get the better of a Klingon with a disruptor rifle, more often than not) but it's not a particularly fair scenario. The thing is that Pandoran wildlife could be a pain for any of these three on the ground (probably least so for the Protoss) but the Navi barely managed to rustle the humans off their planet, and these are all much tougher opponents.

Then again, the Protoss homeworld is a jungle world, which the novels state to have a ton of big predators, so the Protoss shouldn't be at too big of a disadvantage. Assuming they don't send in Dark Templar. Now things start to get nasty on the ground.

And if we're going to have the Klingons, Protoss, and Jaffa fight each other, maybe they should be able to call in more starships. Jazz things up a bit.

[Mr. Oragahn]

If a 35m alkesh whose anti-ship weapons are staff cannons capable of blowing up buildings is a tough opponent for a cloaking 110m antimatter-powered warship with a duranium hull, SG is a lot stronger than I think it is and ST a lot weaker.

Well we know from Exodus (stargate season 4) that an alkesh is capable of inflicting moderate damage to a Hat'ak which isn't a small or weak powered ship. I'll see if I can dig up the clip of the episode in question but that will have to wait until later I'm afraid. A bird-of-prey isn't exactly the most powerful or heavily armored vessel in the Klingon navy and Stargate would have to be drastically weaker for an alkesh not to be any threat what so ever.

JMSpock, I don't know about an Al'kesh blowing up a building with its staff cannons.

sonofccn, the Al'kesh that attacked the Ha'tak used two weapons: the ventral staff cannons, and blue bombs, which I like to think were very specific ion/zat bombs.
The Al'kesh remained within the volume of the mothership's shield, so much that it was pointless to raise shields there.

Notice that the staff cannons didn't do much damage. However, those blue bombs, which were never seen again in the whole show, had a sort of splash/area effect, as they produced electric ripples over large areas.
Later on, when we see the Ha'tak, we notice that only its surface is damaged, but the regions that are damaged are burnt and glowing in some places. The damage would only be superficial. The most important fact, though, is that the size of those damaged areas is simply not corresponding to the area of damage of the regular cannons, and only matches the ripples of the blue bombs.

Also, the equivalent of three AMRAAMs is enough to take down a Ha'tak, especially if one lands near the engines. The ship won't explode, but control will be lost.
Plus one shot from a Death Glider into the canopy is also an assured victory against such a ship.
Their shields are atmospheric shields, not battle shields. The only Al'kesh we've seen with battle shields was in Continuum, and that was Teal'c's own Al'kesh, and that's imho solely due to Ba'al who decided to be a little bit more efficient in his tactics this time, after altering the timeline. His Jaffa could also one shoot a man over a 40~50 meters distance with a weapon staff held at the hip.
The shields of the Al'kesh were used to protect a Russian building which harbored a stargate. A Ha'tak was firing at it with a low ROF, and that's with yields which I would really peg, at best, at hundreds of gigajoules (although in some other shots they seemed to be worth a couple kilotons, but the movie isn't exactly stellar in its consistency on that point).

I wrote a lengthy post about the shortcomings of an Al'kesh, and how it could be turned into a real warship here.