This is my first real post so here it goes. I am a noob at these led flashlights, they’ve come a long way since I bought my last one about 4-5 years ago. I bought one on Amazon, a 502b and was impressed with the output for hunting. Then I bought another one for my son, not as bright. Both are supposed to be cree xml t6, but one is labeled xml-u2, and its less bright. I dont know if that makes sense. Then I started reading about dropins, can you recommend a good dropin that will be bright. The first light led just says xml and l7, but it is much brighter. I’ve been lurking for a while, and I wish I would have come here first, before buying, would have purchased quality ones. Live and learn, appreciate the help.
This one should be good: http://intl-outdoor.com/xml2-p60-dropin-module-alxm2-p-740.html. Brightest would be the XM-L2 U2 1A with an SMO reflector, and pick your modes. If you want a less "blue" tint, the XM-L2 T6 3C (neutral tint) would be a good choice, sacrificing some output, not much. If you want a smoother looking beam pattern but sacrificing some throw, than choose the OP (Orange Peel) reflector.
I build my own - more powerful than this one though 
.
XML U2 should be more powerful than a XML T6, but, the amount of current they are driven at makes a big difference, as well as the reflector. Some P60's may be as low as .5 amps, while others as high as 3 amps (higher for custom built ones). I like 3.5A, or 3.85A for even greater output but at this high amp level, it produces a lot of heat.
The nice thing about a P60 host is the internal upgradeability. It’s only a few stocks drop-ins, which have their uses; it’s not like you screwed-up on a $150 Quad purchase. The new Ultrafire 502b is a damn sight better than the WF-501.
If the XML t6 is driven at 3A while the XM-L U2 is driven at 2A, it could explain why a less efficient bin is brighter.
XM-L2 (which is 2nd gen compared to XM-L) has plus 20% proficiency. You may or may not be able to upgrade your tailcap with a McClicky switch, which has a spring that won’t melt under high current 5A+. (The drop-in end of the spring may still char and deform though.) Having said that, you can go with a Hi-Cri LED (like a Nichia 219 or XP-G2 Hi-Cri) that maxes out at a lower current, while giving an pleasant neutral/warm tint.
Vinhnguyen54’s custom drop-in link is below. A little more expensive nowadays, but if you order a direct-driven XM-L U3 that drains 6A, he will sent one to you. (You’ll need aluminum foil, a good battery, and a McClicky for that DD beast though.) He also has no-memory as well as a assortment of different LED sizes/tints if intl-outdoor doesn’t stock something you want.
Glad you came out the dark closet. Hang around this is one of the best forums on the INTERNET, and definitely the nicest most knowledgeable flashaholics J) 
Here is a link to study:
http://kaidomain.com/Search/SearchResult.502b/0/1/20/rank?show=grid
Thanks for all the help guys, I’m glad I found this forum.