i grew up on both the marvel and the dc shows... and i gotta say i'd take the dcau any day.
While, it was far from perfect and had its share of weak episodes, it was, all-in-all, a great exposure for the DC Comics characters. Even while going off and putting different spins on classic characters, the DCAU programs still stayed true to the comics' history... it also helped that the programs had impressive animation and wicked writing.
the marvel animated universe (or MAV, as i put it) was pretty sweet as well. growing up, i thoroughly enjoyed the spider-man series and the original x-men series. however, their other shows didn't really fare as well (Iron Man, Fantastic Four, Hulk, Avengers... though i did enjoy x-men evolution, somewhat.)
however, if "Ultimate Avengers" is any indication, Marvel could have a successful run in animated movies, based on their characters... much like the success of DC's "Mask of the Phantasm" and "Return of the Joker."... (note: i will definitely be picking up Ultimate Avengers 2 in August)
the DCAU became a beast of its own, being able to connect over 14 years of continuity ranging from Batman, to Superman, to Beyond, to the Justice League. It was like watching an animated "elseworlds" tale...