I'm interested about the quality of various types of LEDs and about other attributes like expected lifetime, brightness and so on?

The best in the industry by far is Cree. Cree leads the research in optical semiconductors and has achieved higher efficiencies than anyone else using their silicon carbide (SiC) devices. Recently, they just achieved 200 lumens per watt!

From personal experience, Cree LEDs are stunningly bright compared to the alternatives. Luxeon also produces powerful high-wattage LEDs, known for their rebel series. Companies like Osram, Kingbright, and Avago are cheap, but good for the money.

You can find super cheap chinese brand LEDs on eBay and other websites. These get the job done, but are not the brightest and not the most reliable. I've actually had chinese LEDs burn out during normal operation, something you don't expect from a technology that's supposed to last at least several thousand hours under nominal conditions.It is rare, but it happens.

While I understand it doesn't very much answer your question, I find these guys are spectacular. hebeiltd.com.cn/?p=z.pricelist.led.diode All the different brightness and angles are listed. Gives you a good overview of different powers and colours etc that are available, all on the one page.

And cheap as my sister. Both have $25 minimum order.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.