Nobody in their right mind would consider this a sane comparison. The Shure SM58 is NOT the best mic in the world, but what it is, is a standard. A yardstick to judge other mics on, and of course one of the few mics that age is irrelevant. I have one in my mic box that I bought in 1976, alongside ones I bought last year to replace stolen ones. now they've been in and out of music clips a few times, I can't tell which is which. I do know that if the singer drops it on a hard floor, I don't worry. I don't care if they whisper or shout, I don't care if they hold the damn thing near their waist, or shove it down their throat - I can cope, and I know what it will do. The Blue Encore could well sound nicer to your ears. The Shure is bland, solid and unexciting, and that's why professional sound people love it. A known product, easy to EQ and make sound nice on any voice. Clever mics with subtle peaks and bumps in the response may sound nicer initially, but then you discover they don't like monitors, or make people with a gap in their front teeth sound nasty, or any other traits.
Buy a Blue Encore and stick it in your mic box alongside the SM58. Use the one that sounds nicer for each outing. If you can only afford one, the Blue Encore could let you down. The SM58 won't. One is a microphone icon, a real standard to use to assess quality of other mics. The other is a microphone. If I could only afford one mic - NOTHING would make me buy the Blue Encore. I'd bet that in five years time, the factory making it will have moved on and nobody will even remember it.