Here is always how I have viewed the siege political guild landscape.
There are the three main alliances that Hoffs mentioned, and a number of small guilds. I group them exactly based upon the questions I asked, but missed one.
Now these are my thoughts on guilds I have little to no true information on, just based on my observations, so if I am incorrect please let me know.
Again, I group my guilds based on the following:
1. Do you want to RP?
If yes, the guilds that RP are:
CWS
Borg
Blu
(Note that all guilds usually have a player or more that like to RP, but as far as I know, these are the only guilds that 'require' all members to RP).
If no, then any other guild will do.
2. Do you want to pk?
If yes then:
KOC (I do not believe they recruit)
TnA/TnT/AO
Borg
If no then any other guild will do.
3. Do you prefer pvp/pvm/combo? Note that most all guilds are combo guilds and you can find pvp and pvm opportunities in all, but some guilds lean to one side or the other. For example:
PVP:
JSV/SS
TnA
KOC
PVM:
GIL
4. Are consider yourself 'good', 'evil', or don't care?
Evil:
KoC
Borg
Good (Or Anti-evil):
Any of the HHSF alliance guild members, or more particular the White Council guilds (CWS/GIL/WCB)
Don't care:
Circle of flame alliance (TnA/TnT/AO/Myth).
There's a new Anti-red guild, Blu.
Also all of the main big alliances have faction avenues if you wish to pursue that as well.
Then there's the crafting guilds, DTA and STP.