XLR will always directly be better because it is an analog signal meaning that it is not usable by a computer (Analog is a waveform, Digital is 1s & 0s). But depending on what you use to convert the Analog mic signal to a digital signal is where you might lose some quality where a USB might sound better. For example, I use an Apogee system to convert analog to digital and it is by far the clearest, most precise conversion for under $1k and will sound much better than a USB microphone. Some good quality cheap A/D conversion boxes come from M-Audio and Yamaha as well which will get a good quality signal from an XLR microphone.
All that being said, if you are just using it for speech/voiceover on Youtube videos then all that will probably not even make a difference in the long run as these are all things that to an untrained ear (like the average YouTube viewer) will go completely unnoticed and even if you compared them back and forth to them a difference would not be noticeable. So a USB microphone might work best in your case. I am not familiar with the AT2020 as a USB mic but I know that the AT4040 is one of the best budget mics on the market and if the 2020 is anything like that it will do everything that you're looking for and more.