If someone really knows a profitable niche, he/she won't tell you. From my point of view, profitable niches are those which helps readers / visitors, apart from freebie stuff and adult content.
Better go to the niche you are familiar. If you are looking for high pay niche, insurance, loan and finance will be good
www.google.com/trends - shows you the latest trends. Check this site once every day for about a month and you should be able to figure out what people search the most. Then you start your site and write about it, or sell whatever the top searches are.