Imran is the greatest cricketer to come from the subcontinent. There's no doubting that for me.
If I forget Murali's action, I view him as a very effective spin bowler. In the modern era he was only rivalled by Warne as a spinner and in the whole of cricket history he sits in the top echelon of spinners. Sachin is a true great as well, but I think there are plenty of middle order batsmen who have been as good as him throughout cricket history, and even in the modern era.
I would rank Tendulkar as India's third greatest cricketer of all time (after Kapil and Gavaskar). I think Murali is clearly SL's greatest cricketer of all time, but SL haven't produced many to challenge him in their shorter history. Tendulkar has an amazingly consistent record against all opponents in all conditions, whereas Murali's is a bit more patchy. It can also be argued Murali has cashed in against weaker test nations, and his record clearly shows this fact.