If I had to guess... Hunter.

The heavy armor and big gun make this Guardian probably a Titan.

This Guardian's weapon almost seems like an archaic revolver, a stark contrast to the Cylon-like visor.

Another Guardian render, this one armed with another familiar-seeming sniper rifle.

Distinguishing between the three known player classes visually appears to be more complicated than simply examining available gear and equipment. All three classes appear able to carry and use guns, and wear helmets. All player characters are depicted having their faces concealed.

This would presumably be a view from the Tower. It appears to be on the edge of the city, rather than directly underneath the Traveler.

The colored banners seen in this shot and elsewhere may indicate factional associations.

No mention has yet been made of any gameplay mechanic that would involve guild or faction territories, or the taking and holding of territories during solo or multiplayer.

A rearview of the spacecraft shows more than a passing resemblance to the fighters flown by Spartans in Halo: Reach.

...and heads out towards interplanetary space.

...departs from Earth orbit, far above the Traveler...

... approaches closer to the camera...

A ship, presumably piloted by a player, swings around from the far side of the Traveler...

One of only two shots that show natural landscapes without structures, vehicles or characters. The color scheme indicates either a non-Earth location or a significant environmental change.

I can't really decide if enemies have classes like Guardians do, but given that Covenant and Pfhor enemies in previous games also had variations, it seems likely. These might be a major kind of Cabal, or perhaps something else entirely.

The vertical slit helmet here is similar to that shown earlier on a human Warlock character, and the large shield on the left hand definitely evokes the feel of a Hunter from Halo.

...trying to stamp us out for good.

Still no clearer reason why humanity is so deserving of a stamping out.

These "rhino-like" Cabal, looking like a cross between Halo's Hunters and Mass Effect's Volus, appear to be on Venus or perhaps Mars, and in possession of some rather large guns with some rather large bayonets and a considerably larger wheeled vehicle.

Destiny wouldn't feel like a modern Bungie game without some vehicular combat, so here's hoping we get to blow up a lot of these in a bunch of different ways.

... and they're pressing hard against the cit, probing for a weakness.

Much may hinge on what the motivation is for these numerous factions of aliens to be invading Earth. Resources? Living space? Religious significance?

If these aliens did not originate in our solar system, where did they come from, and how did they get here?

With technology so much more advanced than what humanity possesses, of what interest is Earth, either to the invading factions or to the Traveler?