The right tool for the right job.
Against heavy armour I look at max - but against lighter armour - average (and minimum) is more important.
2d6+4 may be preferable with its minimum of 6 versus a 3d6 weapon with a minimum of 2 - making the ave more important. If target armor is likely to be battledress, then 3d6 looks a lot better for equal skill - as the maximum is more important (since average is not likely to cut it - no pun intended).
Anticipated counter armor, range, given skills (etc.) - determine wether average or max is important to me. Thus planet side versus ship board plays a big role for me (ignoring law levels) as well as anticipated adventure...