as i say im somewhat biased (i currently have an X61, T420, X1C1, X1C6, P52s and a Thinkstation S20) there is a difference of opinion online but i personally think the glass touchpad on the X models is one of the best touchpads you can get, im not so much a fan of the version on the lower T/P/E models though but some people love them
case wise i kind of get, it metal is nice but im also a pretty big fan of the sturdy yet light carbon shell on the X models, it never feels weak and has no flex like metal but its much lighter, i always have my laptop with me so having something lightweight is a real boon as im always on the go
the only other laptop i considered during my last upgrade last year was the Dell XPS line which are also a damn fine device
as for linux its come a LONG way generally most everything these days just works, even gaming on a linux system is pretty easy these days, if you use a major distro with a debian/ubuntu base youll likely have few issues. Again coming back to thinkpads lenovo have started allowing you to choose linux over windows on the latest P series laptops, which if your budget will stretch can also have a 4k OLED display which to me would make the P1 pretty attractive if i werent averse to 15" laptops. but for reference i installed debian on my P52s with no problems at all, even the Quadro GPU just worked
also if youre still a little uneasy about the switch to linux you could consider either making your upcoming system a "hackintosh" or run OS X in a VM
its all personal preference at the end of the day though, the right system for me may well not be the right one for you