I'd love to see a lot of progress in neuroscience and psychiatry especially when it comes to curing mental illnesses like anxiety, paranoid thoughts, depression, bipolar disorder, schizophrenia, post-traumatic stress disorder because life can literally be a living nightmare for people living with these conditions and sometimes it's a struggle for them. All other progresses in sciences like transportation or A.I would be great but they will be just a boon to the current system while solving mental illnesses would be a miracle for the quality of life of many persons across the world.  

Mental illneses are usually unrational and science can usually solve these problems through many trials and errors but some people don't have the ressources to get treatment either because the country they live in has no social safety net like in Afghanistan or they are not rich enough to obtain a treatment even if they live in a wealthy country with cutting edge science like the United States.