Learn what you will work with. I work with more PLCs than I like to (Siemens,Omron,AB,Schneider,Mitsubishi) but have no choice but to learn at least enough to troubleshoot and do some minor modifications. I started out with Siemens and hated it at first and now that I got to know it somewhat well I now hate Omron
because the environment is very different from TIA but a lot of the equipment I'm dealing with these days and for the next few months to a year will be predominantly Omron stuff so I have no choice. I program in ladder and SCL depending on what I'm doing. I even spent the time to replicate on Omron some of the reusable blocks I developed on TIA.
I drew the line at Wago and Sigmatek, there's just not enough of them out there that I don't want to know anything about them and rely on OEM support for troubleshooting.
Future proof isn't something I'm familiar with but the more you know the more valuable you will be.