As an aside, I get what you mean in the context of my earlier comment, but just to clarify for anyone reading, you can use alexa and Google home devices with home assistant (eg to send commands and as media players, I believe), but you can't "deamazon"/"degoogle" them and just use the hardware with home assistant, which would be great if we could!
Beyond that, I assume there's some confusion about what each can and can't do? I certainly can't remember which is which... But I don't actually own one.
Here's what I learnt: Green is the new plug and play server. Easiest to setup and will cover the vast majority of what you'll want to do. Yellow is basically green with a couple extra things built in (namely zigbee and thread), plus expansion bays, if you anticipate building on to it, but it requires you to flash it so less user friendly setup but easy if you're a dev.
But most people start out by using an old laptop or PC sitting around. That's what I did, the got a yellow.