Pick anything that's still heavily used today, that has been around for 10+ years, and it's hard to go wrong. The only caveat to this is on the front-end JS si

Pick anything that's still heavily used today, that has been around for 10+ years, and it's hard to go wrong. The only caveat to this is on the front-end JS side of things. jQuery is still solid, but the language and ecosystem has been so not great over the last decade that something a bit newer might be worth looking at (maybe look at 3-5 year old libs/frameworks instead).