Most people are saying that the Hive will be hardest because of sheer numbers. Honestly, that never stopped me from getting to round 70+ solo on Black Ops 1 zombies. Hive will be easy because of their numbers. Now, anyone who has played Borderlands will know that bigger ALWAYS means worse. much worse. coughbadasspsychoscough.

Just based on some video footage, it seems like the Hive are crazy fast and move in mass numbers, so I think they might be difficult.

I think all will have an equal difficulty, just a different style of difficulty, like hive being weeker, but have a higher number, while cabals being strong but fewer at a given point in time

It's an interesting question to be sure and I don't see the answer being something this cut and dry. This is going to break down to tactics and race qualities. Cabal look to be a combination of squad based tactics and something kind of like blitzkrieg tactics using the shields and heavy armor to push forward. We also don't really know anything about what kind of vehicles they're going to be sporting ether. We do know from the art and such that they'll feature rolling bases much like the sand crawlers from Starwars. These will likely be something like gunboats where we're going to have to face elimination of many gunners before we can really engage the foot soldiers. Vex are rather interesting in that they appear to be a combination of precision drop tactics and high tech emphasis. I imagine we'll be seeing more limited numbers out of them, but they'll hit for some rather critical shots. As with the Cabal, they seem to not be showing any vehicles for them. I see them ether not using vehicles or their vehicle units will be a unit rather than just mounted. The Hive will probably be one of the more in your face ones out of the group. We know that the basic troops mostly will feature unarmed melee units that are more animalistic than anything. The race also sports a high population emphasis as well. We're probably looking at something approaching Zerg qualities. The casters are going to be interesting in this one due to the unknown factor from them. They can possibly play def, support, or offence. We may even see them broken up into their own sub category based on those qualities as well. We also have to consider the knights in this. They look to be very heavily armored and brutal, but I think they've melee based. All the shots I've seen show them with a sword and no other weapon that I can see. I'm guessing that if you get in melee range they're going to wreck, but with any kind of range it'll be like killing the melee units in the Gears of War games. The Fallen stand out as the least extreme of the four. The grunt units appear to sport light armaments and lack refinement in tactics. As we've seen from the E3 video, they appear to be easy to take out and not the biggest threat. The more articulated use of tech with them as a race on the other hand makes them a bit more of a threat even in the grunt area. With deployment of the Shanks among other goodies, even the easy to drop units may be a bit more lethal than they let on. The captains could prove to be interesting but familiar. This is Bungie we're talking about and the captains movements and tactics feel a lot like a reskin of the elites. That being said, if that is the case we've done these fights before and are all too familiar with them. It's the use of tech like Devil Walkers and the fleet of ships that they apparently have that could really make them difficult. I imagine they'll be a lot like fighting the Covenant all over again. This being said, the unknown factors to the other races make them just as dangerous as the ones we do know about. The tactics afforded to each race promise to make them a different challenge in their own distinct right.

Fallen. Primary reason, they like to get their claws into everything, as pirates do.

Probably the Hive.

I'm kinda torn between hive and cabal...hive because of sheer numbers and variety to the type of enemy....cabal because even their lowest ranked enemies are brick shithouses