Hi, great question, will add this to my guide :)

Turret is the most universal - if you expect a fight for several seconds in the same spot or want to run away due to gank, you can use this one. It slows enemies without having Rylai, has quiet good damage over time and is a nice addition to other turret's damage. You can also use this turret as a way to zone out enemies that are comming to team fight

Rockets - it is burst damage, if you see low hp enemy and stun them correctly, you can use this R to kill him. You can also do some trap - 3 turrets in a bush, if you land a stun and add R rockets to it, you can instakill some squishy targets. Don't use it in team fights, unless you catch enemy adc / apc that can be killed. Turret is better in most cases

Granade - it is a great way to stun enemies in TF - if you see an opportunity to stun adc or some really imporant target, you can aim at him. You can also try to stun teams that position badly, so you can stun multiple targets. You need to calculate if you want to use turret for damage or granade for cc, sometimes you need damage, sometimes cc