The Trooper Mark III was made only in .38/357, .22 Magnum, and .22LR.
Probably, from a collector's standpoint, the .22 Magnum would be most valuable due to the lower production numbers for this.
The "4 t's" refer to the gun having Target hammer, Target trigger, Target (adjustable) sights, and Target grips.
In fact, the Trooper Mark III only came with the 4 t's.