Like many other issues in morphology, generality or productivity of affixes is relative. The plural (s) inflectional morpheme enjoys a very high level of productivity as the majority of singular nouns are pluralized by the s morpheme ; however, the derivational adverb morpheme (ly) is equally highly productive as well. On this basis, it is hard to assume that of the two categories which one is more productive.

Both of them are importantly productive in English. However, I believe that the derivational affixes seem to be more productive.

Good question, following