I vote for the uncontrolled airport. The smaller the better.
Simply for the reason a student can get more time in the air for his money.
He isn't spending money taxiing a half mile to the active or being number three for takeoff while the clock is running.
At a small strip he could do two or three touch and go's before he might get TO clearance at a controlled airport.
At the small strips you can also get numerous "engine failures" to a touchdown when working in the pattern.
I remember the first time my instructor had me fly to an "international airport". Friendship Airport, Maryland. I never saw so much concrete. I asked him if he wanted me to land across the runway.
After that dual flight I flew into Friendship solo for practice. A student could do that in 1960. No air traffic like now days.