Grunfeld or nimzo

WHAT ARE THE GENERAL DIFFERENCE?

WHICH IS BETTER AND WHY?

I LIKE TACTICS AND OPEN POSITION :) !?

And the caps-lock key.

yes it is ok ...let the caps be on... yea am giving a hint so that if u wanna help me decide which one to choose it is better u know what i prefer...so kingpatzer whats ur opinion :) ?

Grunfeld is more tactical, with more open positions in most/all lines, while nimzo is quite positional and sometimes can get quite closed. I personally prefer the grunfeld, but the nimzo is also a quite acceptable opening.

There are some positional lines that white can play against the grunfeld though, such as Bg5, g3 systems (if black choses the c6-d5 approach), and other variations. However, the grunfeld has a lot of tactical potential, such as the russian/hungarian variations, closed variation, many of the exchange variations or some of the f3 lines, etc.

Personally I don't like either very much, so my opinion won't be much help. The Grunfeld frustrates more as white, but neither gives the kind of positions I'd voluntarily assign myself as black. Of the two the Nimzo seems more positionally sound. Personally, I prefer the slav and semi-slav myself. 

Dutch player here, though I have a Queen's Indian as a secondary.  The Grunfeld is very theoretical.