Call yourself a humanist and you'll be using the broadest, easiest, most encompassing term of self-designation.
Call yourself a humanist, first and foremost.
This classification encompasses all others. After the word “humanist,” you may add your preferred subset label: humanist Muslim, humanist Christian, humanist Buddhist, humanist Atheist, humanist Agnostic. It is important that these subset terms do not precede the word humanist. We are humanists first, and what we are after that is secondary or tertiary or even further down the line.
We are humanists first because we are human infants first, insusceptible to further branding at that time. No infant is Muslim or Christian or Atheist or Conservative or Liberal or American or Dutch or Egyptian or any of the like. An infant is simply human, inducted by that native condition into decades-long participation in basic human goods, chief of which are friendship, play, learning, skillful performance, and the rearing of children.
We are humanists first because humanism is easiest to believe. There are no fabulist doctrines to embrace. No winged ponies. No uncertain nativities. No staggering saintly pedigrees. No demonic possessions. No impracticable moral embargoes. No otherworldly rules about textiles that drape the body. No theistic dietary whims. No lurching angels trumpeting doom. No fiery underworld that brutalizes dissent. Humanism says simply that human ingenuity is the source of goodness and therefore a source of delight. Easy assent.
We are humanists first because, apart from the rough generosity the natural world bestows, humans mold a malleable nature on behalf of human flourishing and create innumerable gracious alterations to the natural world, from a road to a bridge to a house to a plate to a toy to a pipe to a balm to a bed to a flute to a lute to a wending story in florid prose—and a near infinity more.
We are humanists first because with human tools we attempt the anatomy of human destructiveness in order to improve ourselves and shed our vices. With human thought, we devise ethics of urgency, so that we may rapidly arrest rapacity and protect ourselves and the elements and the animals.
We are humanists first because we cannot be reduced to anything smaller than the human, and we cannot be elevated to anything larger. Even the post-human and the trans-human are but species of the human. And from humans come all the metrics of morality, extending to bonobo and cyborg alike.
Label yourself with the broadest, most relevant term. When someone asks, “What are you?” say “I am a humanist.” Search and see what the word has meant. And as you understand it, receive it first and foremost. After this, if you must, you may array yourself with any other supplementary hue on offer. But first, start with humanism.