I'm planning to do HFI Certification, how important is it for a designer (UI-UX) and is there any alternatives for the same?
It is not that important if you already have a lot of design experience. If you don't have much experience then the HFI course will arm you with some useful skills and knowledge. Also, if you are looking for a new job, it might be that the HFI Certificate is the only thing that separates you from other candidates.
As for other alternatives, there are now some very good courses that are focused on UX Design at some of the universities, either at undergraduate level or masters.