>would usb microphones be better?

Yes... in my experience, analog microphones seem to be more susceptible to noise/interference from other electronics in the computer.

Depends . . .

For podcasts and just Youtube stuff than yes.

For professional recording (Making music / singing). 

No. Too much noise will make it hard to mix it properly.

If you are "practicing" rapping or singing, get a USB one. To be honest though, I would still get an XLR mic just because they seem to be the same price these days.

USB microphones are good, but you are tied to a computer. You can also look into digital voice recorders, which would allow you to be more mobile.