Labels exist to give you an avenue for self-expression in a world that doesn't want queer people to express their identity, not for liberal "words mean something" dorks. Does it resonate with you? Then use it, a lot of people go by both of these terms. Nonbinary is an umbrella term to begin with, if your idea of gender is something else then "men are from Mars, women are from Venus and these are immutable, clearly seperate, very real things that totally exist" you're fine to wave that nice flag around in my book.

Nonbinary is both a specific identity and an umbrella term. Agender is definitely under the umbrella.

Non-binary is an umbrella term that encompasses genderlessness, and ultimately, just like Comrade @AcidSmiley@hexbear.net said, labels are personal. The worst part of label discourse is when people try to be so prescriptive with labels. Like, as someone who identifies as pansexual, for instance, I abhor it when I see people say things like "Uhh, you're actually pan, not bi" (or vice versa) to a person who is just aiming for personal comfort in their own label. I consider myself genderless in a sense, but I don't call myself agender explicitly too much. There was a period where I was more fond of outwardly professing "agender" as my primary label, but nowadays, I just use the term "non-binary" and leave it at that because I like broader terms for myself typically. Basically, all that matters for me when it comes to labels is that I feel comfortable using that term and I find that term conveys my sense of identity to other people best. If a label checks those two boxes, it will most likely be at the forefront of my identity, so "non-binary" for gender identity and "pansexual" for sexual orientation fills that role best for me.