Definitely go with T, P or W series. T450, T460 are probably the sweet spot. Also the slim versions (T450s etc).

If space or weight is an issue, X series is ok too : X250, X260.

Digit after the letter indicates screen size: 2 means 12 inch, 4 is 14 “ and 5 is 15”.

Stay away from E, L or Yoga thinkpads. Those are consumer grade.

For micro/tiny form factor, anything is fine. Dell, HP and Lenovo all are great bargains and quite reliable ime.