An Thinkpad up to the 4-Series (x240,t440,t540) can run any BSD, but after that, OpenBSD is your best bet. NetBSD (the one I learned about Unix with) has fallen a bit behind in features and hardware support, it is rarely used for production any more (makes me sad, but that is how it is). FreeBSD has a giant set of features and has the most current and largest software library, yet it does not run perfect on newer Laptops. OpenBSD ist more conservative and very pure, is used in some production environments, is actively developed but has the smallest and least up-to-date software library. So you can choose which disadvantage you can live most with. NetBSD is said to run on the largest number of platforms, but I'd argue that in practice Linux took its place long ago.