"Is/am/are wanting" is an example of the present participle.

Present participles create the progressive tense in English. Some authorities on English grammar call it the continuous tense.

The progressive tense stands in opposition to the perfective tense ("had been waiting," for example). Why English grammarians don't call it the "imperfective tense," like the Russian's do for their corresponding tense is anybody's guess, but they don't.

One common mistake is to consider the present and past participles as "passive" in construction due to their coupling with state of being verbs, such as is, am, are, was, were, have, had, has, be, been, and being. Although, the imperfective feeling of the progressive tenses does give rise to certain sense of passivity, the participle itself does (typically) directly connote a state of action. "I am typing, right now. I am not very exciting to watch when I am typing, but I am acting (sometimes viscously) in my hammering on this keyboard."

That being said, even though participial phrases are "active" by definition, they are still not necessarily as direct in speech as some of the alternatives. Therefore, as a matter of style, they are definitely worthy of scrutiny.

In which case, most writers would confidently say that the two alternatives provided are, in fact, "better." Why they are better is because they are more direct.

(Although, it should be pointed out that "this stuff" as used in the sentence is not at all very direct or clear and ideally should be replaced with more specific language. Though, as for the verb choice, this is literally beside the point.)

As to which of the alternatives provided is preferable. I think this has to come down to the context in which it appears. Depending on the overall tone of the surrounding text, one might very well seem to most readers as awkward, with the other being clearly preferable, and vice versa. And there are probably an equal number of examples where either would be equally satisfactory.