I have a form to create which will have some pre-populated fields(from SP list) , some conditional based rendering  of SP list data and some input fields(data has to be stored in SP list) and also i have to mail this form to some email ids.

As such InfoPath form would be best suited. It will cover all the points mentioned above including mailing the form.

But I have to replace InfoPath.

Any help/suggestion will be most we

This is in the wrong forum. It's not a search issue.

If this is a dynamic form that needs to be filled in offline and then returned via email then Infopath is hard to beat. Failing that you have Word forms which can do the job but aren't as enterprise grade imo.