Someone already said it. Adaptations are always weaker in comparison to its original counterparts. Of course, this would usually be due to the fact that the adaptation, at one point or another, would try to deviate from the source material, thus, the drop of quality. Especially when the adaptation is simply trying to prolong itself to buy time.
If there is one adaptation that I think would be slightly better than the manga, I'd say it'd be Hunter x Hunter, but only because it remained true to the manga, without any filler whatsoever.The soundtrack is also a very nice addition. Heck, even with the manga's hiatus, the anime never dared to continue with fillers. Now, if given a choice between two identical storylines, would one not prefer to see it animated? The only thing I hated about the anime was that they never animated the Hisoka x Kastro fight.
They also removed the Love Love Town from Greed Island, and I loved that part >.<