Reports from google says that Mobile searchers are now more than desktop ones in 10 countries including the US. So, my query is that in your opinion where should I invest more to get a better return?
Mobile search is on the rise and it may have more number of users than the desktop but it doesn't mean that the desktop has totally loosened its value. The importance of desktop search will always remain intact to certain extent. So, if you ask me I will say that you should invest to them equally.
Actually, it depends on the niche you are targeting about. In general case I will say that 60% in desktop and 40% in mobile should be enough.