I've bought three of the 217, because I love it to death. It's good for applying colour, blending eyeshadows, and is my favourite brush for blending out undereye concealer. If I had to, I could do my entire face with an army of 217 brushes.
The 224 can... blend eyeshadows. I have one. I use it if I want a less precise blending out of the shadow I'm using, or, more often, if my 217 is dirty.
I vote for the 217.
