My 2 (non-fiat cuz that's what we do here) cents if it's worth anything...
The best alt coin to invest in is the one that has the best marketing bull shitter out there. Everything is speculative and is sometimes backed by a good theory/technology/(insert another slash word here) that makes people believe in it. Yeah I know I'm going to piss someone off by saying this but honestly, c'mon. If an alt coin can get enough smart people out there to back it, then boom goes the chart. Don't misinterpret me for saying to go with the masses, because that's not what I'm saying at all. You have to do your research, educate yourself, and be ready if it comes.
^^^ all of this is discredited though because I'm a newbie on here.