WLED: Open-Source, software only you can flash on various boards. Doesn't have the scripting/live-coding part that Pixelblaze has (i.e. you need to write your own effects in c++ and compile them in). Doesn't support 2D/3D mappings natively. Has a few more APIs.

Pixelblaze is really nice and in many ways the more advanced option, but for most things I go for a <$5 board with WLED or FastLED over $35 (+shipping +tax) for a PixelBlaze.

I've used both quite a bit for various things.

The biggest differentiator is that Pixelblaze is built around the user being able to define their own patterns, while WLED is more built around getting a turn-key setup as easily as possible. One of the downsides to the Pixelblaze, for me, has been in instances where I just want a simple thing like a specific color, or a simple fade or pattern. While you can do that on the Pixelblaze it can take more time to tweak the PB code vs. just moving a couple of sliders in the WLED interface.

WLED has many really cool advanced features like support for segmentation of one led strip into multiple ones, Synchronization with other instances, Alexa/Google Home support, Phillips Hue Emulation, HTTP API, Controlable over DMX with E1.31 or ArtNet.

There exists even a sound reactive fork. Which analyzes(volume and FFT based) the audio directly on the ESP32.