Healy's position (by extraction) is that Efexor/venlafaxine is the hardest of the antidepressants to withdraw from

One theory is that the relatively short half life of paroxetine and venlafaxinemake these two drugs more problematic. This leads to a withdrawal strategythat advocates switching from paroxetine or other drugs to fluoxetine.The second is that paroxetine and venlafaxine are relatively more potentserotonin reuptake inhibitors and this theory leads to a switch to less potentserotonin reuptake inhibitors such as citalopram

http://www.clinical-depression.co.uk/half_life.htm

Seroxat/paroxetine half life = 21 to 26 hours,

Efexor/venlafaxine half life = 5 (5 to 11) hours