I have a question regarding Qurbani. Is Qurbaani waajib or Sunnah? Is it compulsory to offer an animal for sacrifice or we can instead give away the money to a needy person.
Before answering your question I want you to appreciate that the word Sunnah has different connotations. The term is used to refer to the religious practices instituted by the Prophet (sws) as part of the religion. In this sense, it is used in contrast with the Holy Qur'an which covers the Muslim beliefs. It is basically the discussion of the sources. Islam is comprised of beliefs and practices. The Qur'an covers the former while the Sunnah the latter. Both are, however, equal in authenticity. Both have been handed down by the generations of the Muslims since the Prophet (sws) taught them to all and sundry among the Companions (rta).
Offering sacrifice is a Sunnah of the Prophet (sws) in the sense that it has been instituted by him as a religious practice. This does not, however, define the status of the practice in terms of obligation.
Some of the practices instituted by the Prophet (sws) are obligatory like Salah, zakah and Sawm while others are optional for example saying Alhamdulillah after sneezing. Muslims have always been clear on the degree of obligation attached to these practices for this too has been transmitted by the Muslims as they received it from the Prophet(sws).
However, the terms Sunnah, in the sense you have used it, is basically a term of the Fiqh, a discipline dealing with the legal matters. Some Fuqaha (doctors of legal cannons of Islam) use the term to mean some practice which the Prophet (sws) was reported to have done but which he did not hold them compulsory for all. In this sense it refers to the optional practices. Some of them however, consider it wajib. Thus there is a difference of opinion among the scholars of different schools on the question of degree of obligation attached to the Sunnah. Consequently they differ on the status of Qurbani as well. The Hanafite believe it is obligatory whereas others do not.
We believe that thought the Sunnah of Qurbani has not been held obligatory for the believers it is nevertheless extremely important.As regards the question of abandoning the practice for some other important work of individual or collective good it is left on the individual to decide. For example one needs to be aware of the importance of this worship ritual and should try his utmost to offer an animal for sacrifice but he may sometimes while intending to do this abandon in order to fulfill another urgent obligation. For example if I have some money saved for the purpose but am approached to by some friend or neighbor who has to wed his son or daughter and he is really in straits enough to discharge this duty I may try to help him out leaving the offering. This is not standout to given priority to that matter over the ritual of Qurbaani rather it is a proper response to a more demanding situation. God the Almighty is extremely merciful and He may reward me on both the acts, the one I intended in the first place, and the one I have opted for realizing the gravity of the matter. This should not be taken to mean that I give no importance to the ritual of sacrifice or consider it a wasteful activity but it should be read as my proper response to a needful event. This is how we behave in our life. Many people try to save money so that they an avail a hujj journey but cannot do so in the face of some urgent and more important personal or social need. We cannot however draw a principle from this example and say that offering an animal for sacrifice is rather a useless act and we should look for spending in some other cause. We need to fulfill both kinds of duties and it is only when we have no way out regarding another problem when we can postpone sacrificing an animal.
 In the terms of the doctors of legal canons of Islam we can say that it Sunnah. These scholars use the term Fard for something which is obligatory of first order and waajib to connote something that which the Qur'an does not oblige us to but the Prophet's perpetual adherence raises its status to almost near Fard and the third category is that of the Sunanh which they imply to mean the optimal.