This is a hard choice. Each one has its pros and cons on what it will do best.
RE20 comes with a built-in pop filter and the capability of being folded up, making it perfect for musicians who only have room (and pockets) for one microphone. It also has a good sensitivity to transients, so you can get some crisp bass notes from your vocals. However, like most condenser microphones, it doesn’t quite have the warmth of tube microphones but does come close sometimes when all other conditions are just right.
Let’s talk about the build quality of the RE20. It’s a lot sturdier than the SM7b, so you don’t have to worry about it falling apart in your hands. If you are thinking about moving the microphone around and putting it in different places, this is definitely a better option because of how durable it is. Its cardioid pattern also makes it a lot more versatile since you can use it when you don’t need the extra warmth (which won’t be often) or the noise rejection (which will come more handy).
Finally, its design allows for good screen isolation from other sounds around the microphone.
SM7b, on the other hand, is a lot different from the RE20. First of all, it’s cheaper. Second of all, it doesn’t have any built-in pop filter and can’t be folded up. It also has a lot less self-noise and better noise rejection properties than the RE20. However, it seems that its high output is what causes pops. Also, ITS has a lot more issues with backgrounds and extra sounds around it because of its high sensitivity/impedance mix. This can be solved by using an attenuator on it or by changing the microphone’s position in relation to your music sources since this seems to affect the SM7b more than other microphones of its kind.
The build quality of the SM7b is a lot cheaper than the RE20’s. It’s also not as sturdy and fragile compared to the RE20. However, I’ve heard some praise it because of its high sound quality and how it isolates people from outside sounds. Even though I’ve had no issues with this microphone, I would not recommend using it in a very noisy environment like a nightclub where people are shouting and shuffling their feet around, especially if you’re trying to isolate yourself from other background noises.
If you need a general purpose microphone that will do both well at different times without fail, then the SM7b is a safer bet than the RE20.