Stop calling me names.
There has been a detailed comparison of the PT-91 to Leo2A4s on NFOW - the PL military forums. They came up to a general agreement that the A4 is better than the standard version of the PT-91 on many levels. I can provide you with many quotes.
Also, you are comparing apples to oranges. PT-91M may seem better than the Leo2-A4 in terms of some upgrades. Overall however, the A4 is still a better tank IMO. The amour, overall ergonomics, mobility, survivability of the crew still favor the Leo2 A4.
This is my opinion and it is a subject to a debate however.
In addition, while the Pt-91M may be better in some aspects than the 80's Leo A4, the Leo2 A6 is much better.
The Poles should purchase the used A4 for as low as possible and then upgrade as many of them as possible to the A5 to A6 standard.
Even if the cost of the modernization is high it still makes sense.
The A4-to-A6 conversion is still much better MBT than the PT-91
Also, the car argument is valid as well. A car technology/engineering/reliability provides for a very good model of overall engineering/construction/assembly standards of the German manufacturing industry.