It’s these sorts of questions that get asked a lot. The most simple way to answer it is, if you like their music, they’re good! Music and singing is hugely based on personal opinion and the beauty of the industry is that nobody likes exactly the same things. Variety is so important.
When it comes to technique, you can indeed tell that some singers are technically better than others but that doesn’t mean that they’re necessarily bad. Make any sense? Ha.
If you were however to copy a singer with bad technique, chances are that you’re going to struggle and potentially cause some damage. If you get to a place in your singing career where you can create the sounds and style you like without damaging your voice, you’re winning. This is everybody’s ultimate goal, right?
Singers like Bruno Mars, Kelly Clarkson, Whitney Houston & Javier are pretty good in terms of technique. You can hear that breathiness or power are choices made by the performer as these stylistic choices are not present at all times through every single one of their songs.
If you listen to Alicia Keys on the other hand, you’ll hear that she is pretty strained when reaching the high notes in her songs. Some of her stuff actually sounds quite cool and this is obviously the sound that she’s aiming for, but trying to replicate that will potentially cause some damage.
I guess what I’m trying to say is enjoy the singers that you like but just be aware that they might not be on form, technically and therefore try not to copy their style. Find your own way of doing things. That’s much better for you!