Due to circumstances I went through a number of driving instructors (also had a couple of stupid old farts who I decided not to continue with after the second lesson) over a period of nearly 3 years (didn't pass my test until I was nearly 20), but the car I spent the most time in as a learner would have been my dad's 1995 Fiat Punto 75 SX.

The instructor I was with the longest had a Ford Escort MkVI diesel. That was the largest car I drove as a learner because in Britain new drivers can't get insured on anything much larger/more powerful than that. All driving instructors over here use small hatchbacks (nothing bigger than a Ford Focus).

The first car I drove as a learner was a Mercedes A-Class (probably an A140) but only had a few lessons before the self-employed instructor got a new job doing something else (he wasn't a very good teacher anyway). The car I eventually passed my test in was a Ford Fiesta MkV (an instructor's car).

Like many I don't think I became a competent driver until I started getting experience driving unsupervised after passing my test.