Used MacBook - how did they change 2012-15?

I’ve bought several used iMacs of about 5 years old with great succes. Im now in the market for a used laptop but have no experience in this. I’m after a used MacBook Pro or even Air for daily use with no Ned for real power, 8mb RAM and 512 SSD.
Obviously a 2012 model will be cheaper than 2015, so what were the improvements in that time? I see they were speed bumped ‘i’ chips but were these significant?
Anything else to look out for?

The first 2012 Retina MBPs (15") had trouble with image retention depending on which company the panel was used from. As far as I remember, the next generation did not have this issue. So, if you want to go with a Retina MBP, I’d suggest getting one of the later ones.

Besides that, remember that with an iMac, there was no battery which has been used by a previous owner. Depending on use, the difference in battery health between a 2012 and 2015 MacBook will not be insignificant.

I believe the 2012 model was the last one that is fully user upgradeable. I had a 2012 13" and doubled the ram, change the harddrive to a 512 ssd (enabling trim), and replaced the battery once. The 2015 is the last model with the good keyboards. I currently have a 2014 15" 16 gig/512 ssd that I use daily and it is still a fine laptop.

Marco wrote a great Best Laptop Even Made article last year.

If you are looking at different used laptops, I would check the Battery Cycle Count. That would be your best way to compare battery condition.

The 2012 non-Retina model is user upgradable. The 2012 Retina is not (RAM soldered to the motherboard, etc.).

I believe the force-touch trackpad was introduced and added to the MacBook Pro line in 2014 (though I don’t know which generation it actually arrived on, might have only arrived on the early 2015s).

I’ve not used Force Touch as I am still on iPhone 6 and old iMac. My feeling is that it would be interesting as a Mac nerd but not necessary on this sort of purchase.

With the force touch trackpad (introduced in 2015), the trackpad also changed from mechanical to fixed. So those are more reliable since they have no moving parts (fewer things to break). They also have the benefit that clicking feels the same everywhere on the trackpad.