All things considered in a swimming pool, either option will produce a strong shell. The skill and knowledge of the applicator and crew will far supersede any negligible differences between the two.
Shotcrete has the advantage of having larger aggregate in the mix and the yields are typically higher in compressive strength given the same precured cement content. Some may also argue that more pneumatic force can be applied to Shotcrete during application yet produce much less rebound.
Shotcrete can be ordered with the cement, aggregate, and water content (slump) specified which are then measured by a computer and generate a ticket that shows each of those parameters and the batch mix time so you know how long it's been in the truck. On very hot days, plasticizers can be added to replace/reduce the water needed for application without decreasing the ultimate cured strength.
Gunite is much different. It is preferred to have the mix brought dry in a cement truck for the same reasons mentioned above but not all contractors do this. Contrators can dump sand in the street and shuttle it to their equipment with a skip loader where it is then mixed with cement and carried to the nozzle by compressed air. In this scenario the cement/sand ratio is nothing more than an approximate, as is the water/cement ratio as the nozzle applicator controls it basically by sight. The finishers prefer a wetter mix because it's easier to trowel and smooth but this yields a much weaker product that is prone to shrinkage cracks and reduced compressive strength.
Gunite produces significantly more rebound which should be discarded but is rarely done. The rebound is often used in steps and stairs where it will end up causing problems down the road.