Lately we have access to everything. We can hear singers from the past and present in almost any genre whenever we want. This affects our taste and our aspirations as singers.
Classical singers going for training in popular styles want to learn how to belt. A guy with a Johnny Cash voice may want to be able to sing a Bruno Mars song in the original key. People want to cross over every which way, and cover everything they like, but nobody can do it all. There are some amazing chameleons out there, but nobody can sing everything.
It is crucial that you find out what your voice and your psyche like. As you try different kinds of repertoire, see how it feels, physically and nonphysically. Pick music to sing that fits both your soul and your voice. What styles feel like “home”? Sing for other people and see what they think you shine in best. I have found that singers can learn to love almost any style that they can do well.
Everyone knows about the great divide between opera and rock. There is a gulf just as large between gospel and bossa nova, or country and jazz. Some people are able to sing in a couple of widely divergent styles, but some have only one. It seems that Billy Joel, Madonna, Leontyne Price, Luciano Pavarotti, Willie Nelson, and Sarah Vaughan have done rather well sticking to one main thing.
It is easy to say, “Man, I’ll never sound as good as Adam Levine,” but remember that he could just as well say “Man, I’ll never sound as good as Sam Cooke.” Or Diana Krall might wish she could belt like Jennifer Hudson, who knows? Give yourself a break when you compare yourself to others. If you cover famous songs, give yourself permission to NOT sound exactly like the original. The result is a lot more interesting and satisfying for everybody. When you are more you, and keep becoming a better you, you bring a special quality to a song that no one else before or after ever will.
“There is a vitality, a life force, an energy, a quickening that is translated through you into action, and because there is only one of you in all time, this expression is unique. And if you block it, it will never exist through any other medium and will be lost.” ― Martha Graham