Well, this is something I've been looking into for my current build, so I'll share what I picked up from shopping for generic addressable LED strips:
There's three models of strips commonly being sold on t'internet, WS2812, WS2812b and SK6812. The WS2812 are older, so they can be found cheaper, but they're really not suitable for duelling sabers. That's because all the data goes through the LEDs in one line, so if one pixel dies, all the pixels above it die. Ws2812b strips are an upgraded model with two data lines, so if one pixel dies, you just get a dead spot on the blade.
WS2812b strips are the most common of the generic addressable LED strips that I was able to find on sale across the internet, to the point where the WS2812b name has become a bit of a generic name for all addressable LED strips. The catch there is that sometimes, you'll find less scrupulous places selling WS2812 strips as WS2812b strips.
Then there's the SK6812 strips, which are a more recent version. The main difference is that while WS2812s have RGB dies for colour mixing, SK6812 have an extra white die to the LED. that die can be either cold or warm white, usually advertised in the listing as RGBW (cold white) or RGBWW (Warm/Walter White). They run the same control software as the WS2812b strips, so you can solder one onto the other with (theoretically) no problems.
Oh, and where possible, try and go for a strip with a white background rather than a black background.
As for buying, I went with eBay, mainly because they were cheaper, and I could buy from a UK seller and have options to return them if things go wrong. But, if I'm honest, most of the usual saber retailing specialists have strips at a price that's only a little above what ebay was offering (my usual go to, JQ Sabers, was only four or five pounds more expensive than eBay. I skipped them because I would have been crucified on shipping, as I also bought a high drain 18650 to power them)
Folks I know who dabble with addressable LED strips for non-lightsaber purposes pretty much told me to just buy them from alibaba, but the saving in money was offset by long shipping times (estimated ETA, mid December-early January, no returns), and I kinda want to finish my current build before Christmas, as it's my present to myself.
I would definitely recommend not buying the "proper" neopixel strips from Adafruit, unless you have some very deep pockets.
Anyway, that's all I know, hope it helps.