I currently have a 2015 13" rMBP and am thinking of selling that and going for a T440s (Or maybe a T450s if I can find a decent spec'd one on eBay) and I have owned a T420 in the past, which is still a fantastic laptop if you can pick up a cheap used one. Also had an X220 for a short while, again, cracking laptop for how much I paid.
Honestly, I love my Mac, it's brilliant, however I'm primarily a Windows user. My Home PC is Windows and the only Mac/Apple device I have is my mac. Which is okay, but I'm forced to use Windows applications for my degree, making having a Mac more of a hinderance than a help. Having to use Parallels to run Windows is a less than ideal situation, and not to mention the battery life is awful while doing so. It doesn't run as well as I'd like it to and think I might as well go for a Windows laptop. Boot Camp was an option, but then I was questioning why I needed a Mac if I'm just installing Windows. On top of that, the drivers on Boot Camp in my opinion aren't great at all, the trackpad being one of the most annoying, seems to have a laggy delay to it when clicking things.
The T series from Thinkpad are an excellent balance between portability and battery life. The X series is nice too, though having the slightly bigger screen real estate is nice to have when you need it.
Dell XPS 13 was a big contender too in my eyes, but I ordered one of them and didn't like it at all for a few small reasons, plus Windows 8.1 didn't contend with scaling half as well as it should due to the higher resolution display. Ended up returning it.
Anyway, how are you finding the T450s?