How would you say the following questions:
What/which Mac OS X version do you use?
What/which graphic design software will you use?
I have read "Which" vs. "what" — what's the difference and when should you use one or the other? and the remark of the main anwer:
requires a choice between a number of items.
but here it seems to be an implicit choice between a few popular items (such as Photoshop, GIMP, MSPaint, etc.)