owner of over a dozen thinkpads here (over the last 15 years)

from best to worst of the notable ones:

t420s: needed a fan swap and repaste, but after that was exactly what I've wanted in a thinkpad. Reliable, good keyboard, never had an issue.

x230: keyboard modded this guy but kinda wish I hadn't. the original keyboard was just fine. Still my shop computer, running netbsd now. Probably will outlive me.

t61: My first thinkpad. Got me through college and built like a truck. Core 2 duo felt like a timeless processor that wouldn't ever die. It died in a massive flood after being submerged. I have thought about buying a new t61 a few times. This thinkpad idled at the lowest temp of all my 'pads, often around 25C during normal note-taking workflows with the fan off.

there's a gap here before the next in the tier list

x61s: got this because I wanted a small 4:3 thinkpad. Always a little warm while running, and fan tends to go on even if it's not under load. Chassis more fragile than the above and I managed to break it near the expresscard slot. Screen is worse than the others' already mediocre screens.

x200t: also warm, top-heavy (like the screen part weight way too much). Otherwise pretty nice. Great keyboard.

x270: daily driver to this day if it has 1080 panel. Fan stays off if not under load. Very weak processor, comparable to the x230 desu. For text / emacs it's find though. Keyboard also not as good as x230.

e14 amd gen 2: amazing performance : price. Fan never goes on, runs games just great. Feels like an imitation thinkpad made by apple. Metal chassis but that feels like a downgrade from older plastic ones somehow. Died from spilled coffee on the keyboard :( was a good buy at $200 and I'd rec it to a student to this day.

t41: I'd use this if I could put modern internals in it. Ran hot and the CPU was sluggish even for basic tasks. Built like a tank. I think before the t60 / x60 / Core duo line is where you can't run modern OSs anymore