i am planning to buy a new racket, i am confused on what to buy stiff or medium flex racket for an offense.
Get as stiff a racket as you can flex (during swinging to hit the shuttle). So I would say that it depends on your skill level. Generally the less skilled you are the more flexible racket you should get. From looking at your other posts I assume you're looking at either AT500, AT300, or MP30. The AT500 is still reasonabily stiff but i have never tried the AT300 or MP30, but I would assume they are more flexible.
At500 is quite stiff as the above poster mentioned. At300 is about as stiff as at500 although the specs stated it to be medium flex. At500 is head heavier than at300. If you are of intermediate level, at500 is suitable for you. Otherwise try getting mp66 which is very flexible and head light or other lower end racquets. At300 is not a suitable choice.