All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
According to the view of the majority of the scholars offering a sacrifice in 'Eed Al-Adhha is a recommended act. However, some of them are of the view that it is a Waajib (an obligation). You are permitted to give its value in charity but it is better to slaughter as this is the Sunnah of the Prophet and the Sunnah of the rightly guided caliphs . Had charity been better than slaughtering, they would certainly have given charity instead of slaughtering.
Reviving a Sunnah is better than all other voluntary acts of worship.
Nonetheless, if a person can combine between offering a sacrifice and giving charity for his Muslim brothers, then this is good, but if he is unable to combine between the two, he should offer a sacrifice as a way of following the Sunnah, and then give charity whenever that is possible.
The excellence of offering a sacrifice is limited to a certain period, but there is plenty of time for giving charity [its time does not end].
Allaah Knows best.