What is the best model of used ThinkPad to purchase?

I have a T480 that I'm very happy with. With shipping I paid a little under $250. It came with 16GB of RAM and a 256GB SSD (which I replaced with a larger one).

T14 Gen 3. Or T480 for hot swap battery.

X1 Carbon. Buy what businesses buy in bulk. They get it for a reason

I got a nice deal on the x280 and am happy with it, was also looking at the various X1 carbon. Two criteria I had were I wanted USB-C charging (since I have those chargers around and they can handle these laptops) and a single battery (eg. the T470s I have from work is nice but it has two small capacity batteries that each cost the same to replace as the full size single ones in the carbon and x280). One thing to keep in mind is some of the earlier X1 carbon don't support NVME SSD (I think it started with 5th gen?)

Edit: another thing to consider is soldered RAM. Part of why my x280 was cheap was it's only 8gb and can't be upgraded. Since you're looking at lighter weight things and using FOSS (and perhaps open to tinkering with things like ZRAM) that might be a useful aspect to focus on because there is probably a glut of such machines given how memory inefficient things are lately with every trivial app running a whole browser engine. OTOH, depending how many tabs you tend to have open and how many electron apps you tend to keep floating around, 8gb might start to feel cramped. Especially if you think you might want some VMs around.

T480 can be had on eBay for 200-300 bucks and will perform very well in modern applications. I've seen a few that are banged up pretty bad for under $200, if you're cool with a well loved laptop.

t430 runs great for me but if you need more (stock) performance maybe the t480?

Also I heard the thinkpad golden age was around pre-2005 when ibm was in charge.

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For me, the X270 ist the sweet spot: it is small and portable and has a acceptable battery( in fact 2 of them). The display is usable and comes in full HD. 720p is a little bit too low for my tastes. You can upgrade the RAM and put an m.2 ssd inside(although only with 2x PCIe bandwidth). You can also charge it with USB-C. With an i5 it goes for around 200€ in Germany. US prices are usually lower.

I've got 4 of them, 2 t450s, one that's 8 years old and one that's like 2 or 3 years old, one t560 that's probably about 5 years old and one x260. I'm not a gamer so my spec requirements are quite a bit lower than you if you like to play games with demanding rendering settings.

They all have good CPUs, onboard Intel graphics and 16GB of RAM. All but the oldest one have a 4 core Intel i7 skylake and the older one has an Intel core i5 4 cores, I think ivy bridge. It's the slowest and lowest spec of them all but it still runs like a champ.

I used the older t450 for many years as my main machine, it served me well. Gave the newer one to someone in my family to use, they like it. Tried to migrate to the t560 for my stuff because bigger screen, numpad and all that, and I'm always reminded why I don't like big laptops after I start using one. The hinges are prone to loosening because the display is so heavy, the thing is cumbersome to use when writing code, especially somewhere other than my desk.

I moved over to the tiny almost netbook sized x260 and I'm loving it. The thing has a good CPU and lots of memory, and a secondary onboard battery. I'm a big fan of small machines that pack a punch. The keyboard is kind of small but I find that's actually easier than one that's a little too big, for me personally. It's also just a little spongy and not quite as good quality as the keyboards on the other machines. The display is ~750p LCD and I'm happy with that, I've never been too keen on the constant resolution increases in displays, my ideal is 1080 but I do not care for 4k and have never had a 4k display or any interest in one. I'm happy with the display, the rest of my machines all have a higher resolution display and I still prefer the little guy. I was considering picking up a higher resolution panel for the thing but it's just not that big of a deal to me, the display would cost more than I paid for the machine.

More expensive business-class laptops, like the T-series, is I think what RedHat and others give to their employees, thus they are usually better supported than cheaper consumer models.

I have the x230 and like it, but I'd love to have a t420 for the meme

T-580 & T-590 are garbage builds, flimsy AF both running tuned back 8th gen Core i7.

I still have an x220 that's in good shape, and both my T15(g1 & 2) are solid builds. T15g1 has a larger battery and a brighter screen than the g2.

Literally just bought what I believe to be last generation's X13 on ebay for half the price of the new one. It's been great so far, especially with the power efficiency of Ryzen CPUs. My one complaint is the soldered RAM, which judging by the new lineup is getting phased out, thankfully.

Also fan fact the thinkpad has been used on the iss.

I don't see my model (P15) mentioned tht often,and not sure what specifically. But 'm super happy with mine and got it for roughly 500 euros.

X1 for ultra portability.

Otherwise, T14 or T15.

I just got a Gen 3 T14s and I have been very happy with it. It seems like it has kind of narrow viewing windows which is kind of annoying, but not a dealbreaker for me. Overall a very peppy laptop.

T480 is generally a good bet. I (naively) got an X1C6, thinking that all thinkpads were nice and repairable. The X1 series, at least, is not

Go for P52 if you are serious about FreeCAD.

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Yesterday I started looking for mini pcs and found this post https://www.reddit.com/r/MiniPCs/comments/1afzkt5/2024_general_mini_pc_guide_usa/

They shared this link which contains data on 2.8k machines, it helped me compare some of the options I was looking for and find new ones.
https://docs.google.com/spreadsheets/d/1SWqLJ6tGmYHzqGaa4RZs54iw7C1uLcTU_rLTRHTOzaA/edit

Sadly it doesn't contain data bout the ThinkPad, but I might as well share in case you're willing to consider other brands.

Edit: Oh, wait, I was thinking about a ThinkCentre, not a ThinkPad :P
Well, I'll leave this around in case someone finds it useful, hehe.

I have seen a ton of P52 laptops used in the architecture and engineering industry. I would lean that way or a more modern option depending on budget. P1 laptops are also pretty cool. Not as powerful but more portable and slimmer.