Which disc lock for 620?

[racerx454]

I have settled on a 620 Capirex and would rather I be riding it than a thief, so I need a recommendation on a disc lock.

I have read a good things regarding the Xena brand and was wondering if any current 620 owners are familiar with the most recent offerings.  In particular, I am looking at the XX15, XX14 and the XN series.  My questions are which ones fit best and are the most secure?

Thanks y'all!

-Kevin-