90% or more of the fandom stands behind Enjolras as one of the, let's say, top five best characters of the story, and maybe 25% of the fandom actually cares for Marius.
But I have substantial(by what I mean-- produced from the recesses of my cranium) evidence that they are in fact both awesome, on a fairly equal level.
(If you want a post defending poor Marius, I recommend reading this.)
Fundamentally, Marius and Enjolras share a similar character. Both have something they are extremely passionate for and forget other important details of their lives amidst their love for this object. Enjolras is burdened with a heavy fascination for France, her freedom, prosperity, and political wellbeing. Marius is consumed with romantic sentiments for Cosette.
Of course Enjolras is a political activist while Marius is a lovestruck romantic, but we'll keep the "something they're passionate for" comparison for the purposes of this post.
The thing about Enjolras--and let me say this in as polite and respectful manner as possible--, is that he doesn't live long enough to display too many irritating elements of his character. Furthermore, he's never placed in a position to be very annoying to the reader. He's flatter as a character than Marius is, due to the unvaried settings of his role in the story.
On the other hand, Marius, on account of his extended lifetime and the circumstances Hugo's pen placed him in, lands in a few too many opportunities for facepalming. I don't need to remind you of his repulsive treatment towards Valjean after his marriage. I bet he could win the world's worst son-in-law award. ;)
Where Enjolras has just a few awesome qualities, Marius has pages of flaws and a handful of solid virtues.
He did save all the barricade soldiers at once, go to lengths trying to defend Valjean from Thenardier's clutches, give repaying Thenardier's "kindness" during the Battle of Waterloo a high priority, and try to reunite himself with his grandfather.
He's kind, earnest, and absolutely devoted to whatever he's working on at the moment, whether that be pursuing Cosette, comforting wounded Eponine, or protecting his brother barricade boys.
Marius lives in a world of his imaginings, but Enjolras is in a foreign realm of perfection. The latter is passionate and passes quickly while the former can and should stick with the reader for his determination and amiability, once you wait for him to get himself together. ;)
Conclusion: They're both great characters. Marius could benefit from having his ears boxed and Enjolras should have condescended from his political dreams to the realities of friendships and individuals, but we can love both of them for who are they are. :D
Or at least I can, and maybe I've convinced you to as well.
Do you have a preference for one over the other?