Depends on what you're looking for (from an American perspective).
Comedy from Japan is hit or miss, especially since some of it doesn't translate all that well. Action is usually better, though your mileage varies much more with the budget. Some good examples of drama, since there is a strong market for adult-focused japanese animation. Artwork tends to be stronger overall, though likewise very dependent on budget, and is more than a little homogenized.
Cartoons in the US usually (with some exceptions), are geared more towards kids, and don't tend to have a budget unless (or sometimes especially if) they are a brand. As such, most are pretty unsophisticated, and those that aren't tend to be comedies. Few dramas. Animation almost uniformly minimalistic, though a greater variety between studios.
In terms of movies, I'm tempted to rule for the US. Part of that's probably a lack of exposure on my part, but Miyazaki, who gets perhaps the most recognition, I find decidedly hit-or-miss.
In terms of non-feature animation...Japan. The US has some great series, but there simply isn't enough variety. There's a fair degree of sameness in the Japanese market as well, but there are also a lot of standouts.
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