In all honesty I think TP are on the quality decline - it is getting closer and closer to Lenovo in quality.... It used to be a lot better.
Lenovo has several ThinkPad lines (as well as other laptop lines - IdeaPad, Yoga, etc.), for example the E-series ThinkPads are "entry level" and lower cost - the T-series ThinkPads are the equivalent of the older IBM ThinkPads in terms of build quality. If your ThinkPad is going to essentially be a desk top replacement, an E-series is more than adequate, and you can get a "higher spec" E-series at fairly attractive prices. If on the other hand, your ThinkPad is going to be contantly on the move, out in the field, up in a cherry-picker bucket - you want nothing less than a T-series, an E-series will not withstand the "rough & tumble".
If you need or want ISV certfication, you'll need to look at the P-series, and also be Prepared to Pay for it - many of the higher spec E-series will perform admirably at an affordable price, but they lack the certification and you may be told by support that they are not supported for the application.
Yes - I am biased - I've been an "on-site support" tech for the last four decades or so and certified by the big three (Dell, HP/Compaq & IBM/Lenovo) to provide warranty support on their products. As on-site techs, we see more product with problems than the average user, and we also interface more frequently with the support structure than the average user. We know what works & what doesn't and we "vote with our wallets."
For what it's worth - standard IBM issue to their "Customer Support Representatives" is a T-series ThinkPad - at this time, it's the T480.