There are basic needs: clean water, clean air, infrastructure, transportation, logistics, etc., etc. And also "non-tangible ones". You can get much more authentic social respect if you work on products/services that people unambiguously like and need.
I recommend, for example: - Biomedical: signals, images, ... (I've done a bit) - Anything GIS, urban/transportation planning, geo-spatial analytics, cities, etc. (my chosen specialty, very fulfilling).
There's lots of number crunching, but also human-entry string processing (fuzzy matching, etc.). Actually, very versatile programmatically. And then there is fast graphics (OpenGL, etc.) - not my favourite part, actually, but you can outsource it partly.
You get to work in very multi-disciplinary groups, so you can really assess where you want to go long-term. I was surrounded by people with very similar training to mine - technologically it was pretty good, but topic-wise it was a bit of an echo-chamber.