Don't have the XM-3, but I am partial to AA lights (and rechargeable models) in general, and the LX 3.0 has become one of my very favorites. It is my best and most-used light for illuminating the trail and the woods on fairly lengthy nighttime walks on our ranch. It puts out a LOT of light, and gives me a very secure feeling, illuminating as far ahead and to the sides as it does, as I'm traipsing through some high grass or woods on a dark night. I carry a SL Strion in the other hand for distance spotting (critters and such), and so far, I find this to be a great combination.
It dims slowly and evenly over many hours, and, for my purposes, it is good that it's not regulated, since the last thing I want is for it to suddenly run out of juice in the middle of a hike when I'm far from the house. The LX 3.0 gives me lots of warning before it goes black! I am probably at ~6-7 hrs. on current AAs, and still have plenty of output for my needs. (When I finally decide to load fresh AAs, the tired ones will go to my Gerber/Infinity Ultras, Ultra-G, and Tasklights. They'll stay powered for years!)
I strongly prefer AA lights over CR123s, since I'm cheap by nature, and the LX 3.0 shows the advantage: at ~$.27/ea. (w/ tax) for decent alkaline AAs from Walgreens, and with 3 of them keeping my LX stoked up for at least, say, 7 hrs., that's less than $.12/ hr. Compare that to most CR123s! Even the Inova X5, at ~20 hrs. on 2 CR123s, doesn't do as well, and doesn't come anywhere close to the LX's throw and spill.
At around $40 + ship from batterystation.com or islandsecurity.com, the LX 3.0 is a tremendous light for the money!