depends on what sound u looking for.
at first i bought my zoom g9 was because of kiko loureiro and michael amott are using it.. big fan of them..
the korg ax3000g is more for rock and blues lah..the distortion is really limited.. not for metal players..
X3 live..havent tried.. too expensive anyway..
GT8 is good.. very powerful stuff.. the tone is confirm good.. but i choose zoom because its cheaper and has that double pedal thing which u can do a double whammy or adjust 2 parameters at the same time.. but after i bought it.. haha.. i never use the double pedal at all!
would really like to smell how GT10 smells like though. can't afford to play them.
tonelab LE also good for tone..but not for really hardcore metal kind. distortion is quite limited again..compared with boss or zoom.
but i feel that tonelab SE has the warmest and most natural sounding of all. too bad i dun think its available anymore.
basically zoom stands for cheap and heavy metal.
obviously i vote for zoom.
oh ya dun believe in vox or zoom rubbish about having those preamp 12ax7 tubes.. its complete rubbish.. a tube needs to be driven at very high voltage.. the higher the better.. can go up to 600volts.. so examples like the coltron pedals that work on AA batteries.. or G9 and LE that works on a 15volt adaptor..the tubes are only as good as a lightbulb.. hahaha!
i think i might get my ass screwed by zoom and vox!
good luck in choosing your effector though!