If you are a full stack developer then consider that the Web front end will always be best implemented in Javascript. If you intend to focus on developing server side code (APIs etc.) then either Java or C# are great choices but first look at what libraries/platforms are you planning on using before selecting which one to learn. If you are interested in Data Science and Analytics, Python is your best bet. BTW, I do some full stack development in Python and I find it limited in capabilities. But it is possible to do it using tools like FastAPI, Plotly/Dash and Flask.