The APA102 are similar to the WS2801, as in they have a 4 wire connection, "Power, Clock, Data, Ground" The WS2812b only use 3 wires to connect, which makes them easier to use in some scenarios when you design your own hardware. The WS2812 also have a lower refresh rate, so if you move them or are going for Persistance of vison effects, you will see visible lightpoints instead of a continuous light line while the leds move through your field of view.
The APA102 are more expensive than the WS2812 and newer, so if you are a beginner with LEDS, I would suggest you stick to the WS2812b, since there is tons of examples and support for these out there on the internets. I haven't found anything close as much on the AP102 LEDs.
I am personally using the WS2812b for a project of mine, where I built my own controller based on an ESP8266 Wifi chip. I am driving a total of 2590 LEDs with 35 of these small modules using mad mapper and it's artnet support
I hope this helps