Had both. I sold both. The Tavor was a little odd and, being trained on an AR platform, the rifle wasn't very ergonomic for me. The XCR was a almost a direct transition and very intuitive. However, the XCR's weight sucked and it was unwieldy with the long barrel. I just bought an XCR keymod and it is a HUGE improvement. This thing is beautiful, balanced and extremely comfortable. If you are used to the conventional AR platform, then the XCR may be better. Try a shoulder swap on a Tavor once and you will know what I mean. If you only plan on shooting it from the primary shoulder and want to spend some time learning a whole new set of controls, the Tavor is a solid choice.
Here are some pros and cons:
Tavor
Pro
Balance - great for shooting off hand
Compact - has a full lenght NR barrel in a package smaller than a 14" AR
Military service - some will say this is a huge plus
Cons
Trigger - it just sucks, aftermarket triggers are available for huge $$$ and it still sucks compared to other rifles
Weight - it is heavy, but due to the bullpup design it balances well
Ergonomics - it just is plain unintuitive and will take time to learn. If you are not familiar with the AR platform then it is a non issue.
Transitions - I don't care what anyone says, this rifle cannot be swapped from shoulder to shoulder safely. You need to change your shooting position and be aware of the ejection port, etc.
Limited rail space - may or may not be an issue
Accuracy - I found it to be lacking ove the XCR. May be due to the horrible trigger
XCR
Pro
Ergonomics - extremely intuitive, all the controls are where they should be. Everything you could do with your AR you can do with this.
Modularity - plenty of rail space, caliber swap option.
Maintainence - way easier to work on then the Tavor. Field stripping is a little better with the Tavor though.
Accuracy - compared to the Tavor, this is a DMR.
Weight - excellent in the keymod version
Cons
Military Service - it was never adopted
Weight - the older versions were WAY too heavy
Lenght - this is a long rifle to keep it NR
Functioning and Reliability - there have been reported issues and teething problems. I have had three XCR's. One was the first batch in the country. The next was a G revision and finally the current keymod. The first two functioned flawlessly (I haven't shot the keymod yet). The first one had a horrible trigger that slapped and actually hurt. The second one was perfect. The triggers now are a dream.
Accuracy - while not a precision rifle, the accuracy is better then the Tavor, hands down.
Hope this all helped,
Skooch