both seem to be shortrange because they need extrarubies for getting proper range; while other ranged classes have 40 range by default usually
both have a lot of supportabilities
bard is more aoe type while engineer is more singletargettype
bard has more passive skills (damagesong, healsong, anti-cc-song, engineer more active skills (20%more dps bomb, vaccumtrap, various mechanisms,....)
engineer is great in pinning the enemy, but bard also has (different) CCs
bards most interesting cc is the pull-ability which allows you to "reversecharge" enemies; in aod for example this skill is incredibly valuable sice it allows to isolate and kill players one by one
i recommend you play both classes until level 10 or something, this will give you some insight
in total, bard has more skill that are useful for a group (support) imo
(but dont get confused

with all the supportthings, every class can be played as proper dps or singlepvp)
you could also take a look HERE
http://en.allodswiki.ru/calc/ (site requires javascript) to take a look at all the skills, most are imagineable form their description
if you still have questions ask us