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...