There will be two playable factions in stargate worlds good and evil, each faction will have their own specific storyline, there will be other factions represented by NPC's.

This faction will compromise of the SGC, Asgard and Free Jaffa much like in the show:
SGC:
this faction was known as the SGU in the recent trailer, it is yet unknown if they are actually part of the SGC, but it is unliekly that this factions starting point will be at the SGC it is more likely to be at the Alpha Site.

Asgard:
Asgard is now a race, faction and class so it is likely if you pick you're first character to be an Asgard you will likely be automatically selected as each.

Free Jaffa:
It is yet unknown how how the free Jaffa will be represented in the game

While on the good-side the factions will be working together in the show it is very unlikely that the evil side would co-operate if at all, so little is know about this.

OP-CORE
This will be the human darkside, not much is known about this faction as it is not featured in the TV show, it is also unknown if it will be much like the NID or The Trust, however the starting location will be the castles (a SGC run prison.... so it is likely you will have to escape)

Loyal Jaffa
It is unknown how these will be represented in the game, however if it is like anything in the TV series they will be loyal to the Goa'uld.

Goa'uld
Much like the Asgard the Goa'uld are now a race a class and a faction, the playable Goa'uld are no longer acting like gods they will be going out an doing most of the dirty work for themselves, however they will still be egomaniacs.