Both blockchain and AI.
AI - It is going to be used to do varieties of complex jobs such as performing dangerous tasks, automated driving, better elder care etc. So, it has huge potential - no doubt.
Blockchain, on the other hand, has the potential to disrupt many industries. Starting from marketplaces to traditional banking and online communities - Blockchain tech has the ability to disrupt them all and help developers innovate a lot in those areas. So, in the coming few years I expect blockchain tech to mature and finally be adopted on a much larger scale than today.