really there is nothing to much to gain from each of the guilds but keep one thing in mind about choosing one. theives guild generally is hard to lvl up on with their attribute requirements. but you can pay off the price on your head instead of going to authorities. that way you can keep all your stolen stuff and as well your soul gems.

with fighters guild its easier to gain lvls on attributes cause they have common attributes to lvl up on. but you are going to do alot of illegal killing mainly of theives guild members. its a matter of preference but i think i would stick with the thieves guild over fighters guild.

In case you haven't notice, you can become Guildmaster in both Thieves Guild and Fighter Guild.

how both guilds require you to kill quest givers on both ends?

Glad you ask. [img]smile.gif[/img]

First, join both Thieves Guild and Fighter guild at the same time. Do all of their quest and stop when Guildmaster of Fighter guild ( in vivee ) want you to kill Gettleman Jim the master thief ( don't even get that quest ). you can go ahead and do thieves guild quest " Kill Fighter Guildmaster " do so.

after killing Fighter Guildmaster go back to Master Thief to be promoted to Guldmaster of Thieves Guild. then go back to Fighter Guild in vivee and talk to the orc ( who is standing near the fighter guildmaster ). he will then attack you. kill him and walla!! your the guildmaster of fighter guild.