The XM-L2 LED offers .... 1198 lumens at 116 lumens-per-watt efficacy at 3 A, 25°C.
The XB-D White LED delivers 136 lumens per watt in cool white (6000 K) or 105 lumens per watt in warm white (3000 K), both at 350 mA and 85°C.
The above is taken from Cree's site.
It appears that the XB-D is more efficient than the XM-L2 at low drive points. Low drive points are easier on batteries. I don't know how much that matters to SLAs, or Li-Ions, but it is important to Alkalines and Carbon-Zinc batteries.
A few days ago, I bought a $14.97 Ozark Trail lantern @ Walmart. It is similar in appearance to the Siege, and UST. It has a single XB-D emitter cool white. On three D cells, I imagine that it will give similar performance in lumens, and run-times to the Siege, and UST three D lanterns. None of the above are regulated. Since they are not regulated, they can get crazy long run-times, with continually reducing output. this may be great for disaster length power outages, but IMO, not so good for a weekend campout, or a one or two day power outage.
The relatively new Energizer lantern with light fusion technology that zespectre did a nice review on, really is a nice lantern, for a number of reasons. First, the light starts out nicely diffused. Second, it is regulated, and third, the output is variable.
The biggest problem, with lanterns is the amount of glare. It has been many years since I used a petrol lantern, but I recall having to approach it with my hand in front of my eyes.
In my mind, a low glare lantern that emits a fair amount of diffuse light is a GOOD lantern. If the light also has a reflector so that it can be directed somewhat, that's a plus. If it is regulated, that is another plus. Neutral white option, another plus.
The energizer meets 4 out of 5 (it doesn't offer a neutral white).
It seems that this thread presupposes that a super-high output lantern is a GOOD lantern. I don't know, I think that multiple lower output lanterns might be better for lighting an area.