Personal preference really, I've always gone for box out.
It's straight forwards enough though it's a big seal to press in so you need to be careful to get it in square.
Don't skimp and get a cheap one and give the clutch and release arm etc a good check over and replace anything that's even slightly suspect while you're there.
You won't believe how upsetting it is to have the release bearing give out 2 weeks later!