Quote Originally Posted by domineaux View Post
Pros
The AT 2005 can be used as USB microphone and a traditional XLR mic.

Cons
This USB mic does not have a headphone jack to allow you to listen and record at the same time.

The AT 2005 is a versatile USB microphone with useful features such as external volume controls and an on/off switch.
The ATR2100 has a headphone jack built in to listen and record at the same time. The mic is cheaper as well.

Having the headphone jack can be important, especially if you are making connection to an iphone/ipad or other similar device. THere is one headphone and mic jack with these devices, but you may need it for other uses.
I'm confused by your post. The ATR2100 and the AT2005 are identical except for the type of on-off switch, windscreen, and color. Both have headphone outputs for monitoring, although they don't always work very well. Both are USB and XLR.