Sadly, if you google "best led flashlight 2015", at least the first three pages of results are marketing/clickbait pages. The no-name, fake-name Chinese lights have acceptable quality and are low cost $20-50 (superfire, ultrafire, etc.). There are also many, many name brand lights that typically run $40 - $100; they're a little better built than the no names, and have a warranty and dealers that ship from the US. I like Olight and Fenix, but that's mostly because it's what I bought when I got into the hobby in 2007. Above that are the Premium brands, aimed at Law Enforcement, Firemen, and tradesmen, such as Streamlight, Pelican, and Surefire (see where the fake-names come from?).

You're right to focus on LED. The name brand LEDs are Cree and Phillips (and probably others, I'm a recovering flashoholic). Typically, there will be a brand, family, color, and bin/flux. - such as Cree XML T6. Cree's binning is explained here. The bin/flux part of the LED refers to how good the color is, and how efficient (light per watt) the LED is.

Be aware that the no name lights are extremely "optimistic" about bin and light output (lumens) claims. They'll all claim to be T or even T6, but you might well get an S. With name brands, you pay extra, but if it says U4, you'll generally get that. The premium brands spec high bin LEDS, and deliver.

As someone else pointed out, flashlights have different beam patterns than (many) bike lights. You can decide if you want a "thrower" (narrow beam, long distance) or good fill (wide beam). You might want to aim carefully, and perhaps mask the beam to keep it out of a driver's eyes.

If you want to know more, you can fall down a rat hole at Candlepower Forums.

Edit:
Cree XM L and XM L2 are still pretty much hot-shot. XP are similar. A good discussion of the Cree families is here. T6 seems to be the price/performance sweet spot; if a performance bin is quoted, know that P is good, Q is better, and R is best and most expensive.