…which impresses you the most that costs less than $10 and why that is.
Opened ended question.
Are you talking High Lumen Output or Throw, high CRI, 3 volt or 6 volt/12 volt ???
What is the application?
I would go with the Nichia Optisolis SM653-P9-Rfa00 6500K LED. It has near perfect CRI and every time I use them in my triple S2+, it surprises me as to how will it makes the colors pop despite the very cold (bluish) temperature.
I always liked the XPL-Hi 5000K. It’s what I have in my Lumintop EDC18. Combined with the Carlo 10507, it’s got good throw now and quite spilly too. 
Yup it’s meant to be wide open. Don’t care if it’s any input/output. More interested in why you like it so much. Realize that application is a big determinant here and hopefully the why may coincide with an application that meshes with your presumably most important one.
What does an XHP-70 chip cost?
I don't know emitters that well, but I like the XP-L HI as well.
I prefer warm white, though.
I like that the XP-L HI is reasonably bright, it doesn't heat up like other emitters, and it's kinda throwy.
Optisolis, Sunlike, Thrive. Too bad no one will make a mule using them.
Never heard of this particular LED setup before ya mentioned it. All I had to hear was how much it makes colors pop. Now I gotta get one. Wow. :+1: 
I like the SST40 5000k, and I am a fan of the SST70 also. They are cheap, really high output, the sst40 tint is decent enough, but both are a bit green at low power. SST70 has similar output to a 6v xhp50.2, but more throw and no ugly beam. Xhp70.2 doesn’t make the list because it’s over $10, but that’s another favorite, especially when sliced and diced.
For me, the lh351d, despite not being the best at anything, has the best overall performance among 3v LEDs. It can achieve relatively high output, has almost no tint shift, available in hi CRI, wide CCT options, can be found in a great tint, it’s cheap, efficient. The downsides are: high Vf(brightness decreases with battery discharge), flood and a little green in average.
I really like the Luxeon V and V2.
My favourite one lately has been the V2 3000K, for the tint and beam quality, even not being High CRI!
which one impresses you the most?
why do you like it?
I like the one on the left as a bathroom light, and the one in the middle for EDC:
because they have High CRI Ra, High CRI R9, and DUV below the BBL (aka pink tint)
I’m just beginning to but lights with better tint. My favourite was 6500k when I started buying lights. Now I’m a bit more selective, just a few weeks ago I got a Convoy L21a with XHP70.2 in 3000k which I really like…easy on the eyes.
There are a few that impress me on paper but I haven’t seen them yet:
- Luxeon CZ for probably being the throwiest CRI90 LED
- Nichia NV4WB35AM for superb CRI (specced only as 9080 but likely to reach 9890) with high output, efficiency and fair throw.
The one on the left for the bathroom I bet makes your pee look a lot more yellow. 
For the last few years my favorite and most used LED are these 95+ CRI 5mm from rngwn:
As a modder these things are the bomb for solar path lights, night lights, flameless candles, small lanterns, key chain lights… For pennies it’s a joy to spread hi CRI goodness 7-10 lumens at a time! My favorites are the 3400K and 2300K as I found these low light levels work best at the warmer temperatures.
Placing an order cuz these DO indeed der bomb. Thx for the BLF style info! 
It’s definetely a tough choice.
I would probably go with the LH351D as an all around option.
xpg-2 4A bin from CNQGoods / Ric back in the day for a buck a pop on aluminum . they may be too red/ rosy/peachy for some people but every time I use one I kick myself for only buying 10-12? and then screwing around till they were all gone . To me it's one of the best tints out there . But even great tints can suffer in certain reflectors or with lenses etc . It has to be a bit better cri too or I'd probably be knocking it instead of sending out so much love for it ..Early xml 5c tints still have a soft spot in my heart as well ...Nichia 219B 4500k obviously and the 5000K 219C was / is surprisingly nice ....while most 219C's stink up the place(too green)