Just to throw a spanner in the works, is everyone suggesting the AS-K21 as
a primary trainer aware that it is as good as impossible to spin whilst the
CofG is within approved limits? A-S make a spin kit, but this means that if
you want to use the K21 as a primary trainer you need to faff around with
installing weights on the tail before every flight where you intend to
spin the glider, then faff around removing them again afterwards.

The solution my club (Lasham in the UK) has is to have diversity in the
training fleet, although we have the luxury of 600 members, 100 private
gliders and 50 students at any one time paying fees to support all
this.

Our fleet:

9(I think) x AS-K13: Wood, Steel Tube + Fabric. Used for ab-initio
training because they are easy and cheap to repair, plus they spin (and
recover) well. K-7 would probably do just as well for this job.

2 x AS-K21: Used for transitioning students onto glass at a later stage of
training. Also good for aerobatic training, which I think is a point which
has been missed so far in this discussion. Will not spin readily (see
above).

2 x DG-1000: Used for XC and aerobatics training, plus private hire to
club members wishing to go on dual XC flights.

1 x Duo Discus: Used for XC training / Private hire

Anyway, I think the point I am trying to make is that maybe there is not
one particular glider which is ideal for everything?