i think, in terms of mass barbells are, in most cases better....bench presses are better with barbells, curls are better with a straight barbell, deadlifts with barbell, barbell rows, close grip bench presses...and of course squats!
dont get rid of the dumbells though, dumbell presses for shoulders work far better for me than do barbell presses.
alternative d/b curls are another great bicep mass builder, d/b rows are good for the back, laterals are one of my favourite isolation movements..
in short, dont just use one, use both...i personally think when training for mass(which you want, right?) everyone should:
squat
deadlift
bench press
barbell row
straight bar curls
dips
d/b or military press
dont worry about 'feeling the burn' just try to use good form, and add weight, whilst using good form to the above lifts as frequently as you can(every week if you can) But only 1-2 lbs to the bar, even if you can do more...if you go adding 5 lbs in a week to the bar, chances are you wont be able to use the same incerease next week around, or you will probably sacrifice form...stick to the 1-2 lb increase, but dont sacrifice form, if you cant do them properly wait until you can then add that weight and grow!!
stick with the basics, it always works!