T53
It was quite obvious that the T53 was designed "down" to a budget as opposed to the Blanik being a state subsidised product.
However the T 53 was really supposed to be a "basic trainer" rather than a "soaring" machine and therefore its "simple" design would have been quite adequate for its (up round and down purpose)
As touched on before the main improvement would have been its actual ability to be used on many more days than the T21 (without having to festoon it with people hanging on to it).
When you add on the benefit of not having to dress up like a first world war balloon observer in the winter it got my vote.
I also think it would have "upped" the standards for the operation and perhaps given cadets more of an incentive to continue with civvy club flying after going solo.
I flew it as a staff cadet with no prior experience of a modern day machine and could only see it as an improvement on the existing aircraft with no adverse "handling" issues that made it less fun or more difficult.
Air brake and aileron "tweaks" would have come through as required and less people would have left the system.