I have thrown one live grenade,
SFG 87, as a recruit nearly 30 years ago. Plus some smoke grenades and other training pyrotechnics.
(My experience is only as a conscript, not in any way professional.)
I am a shxt bad thrower, never having played any games that gave me the right throwing practice. I had a few comical experiences. One where the smoke grenade I threw uphill hit a tree branch, rolled down the hill, and smoked our own position. Another time I tossed a "thunderflash" - a giant firecracker to simulate grenades - round a corner into a bunker in a trench system. It hit the zinc lined trench sides and bounced back and landed next to my ass. I didn't see cos my head was turned away from the expected blast. I found out at the last moment and managed to jump clear out of the shoulder high trench at the last moment in record time.
Anyway, back to stick vs ball. There is no question that "ball" shape has won over the stick. Firstly, there is less need to throw grenades to great distances since we now have at least one to two grenade launchers per section. They not only launch grenades far, but also with great accuracy.
Stick grenades are not economical space-wise to carry on the person. Also, the handle cannot be too light to act as a "lever" during throw, so they offer a weight penalty.
In Korean War the British described PLA stick grenades as less lethal than their own Mills Bomb. The PLA at the time had dedicated "grenadiers" who carry only bags of hand grenades and no firearm.
One thing ball grenades does is that you can count on them to roll - to varying degrees depending on round or oval shape, and hardness of the ground. The Brits in Korea mentioned tossing Mills Bombs downhill and let them roll towards the enemy.
(Lacking real experience with stick grenades) I guess a stick grenade would roll less distance.
I threw a metal ball grenade simulator during CQB training. Again, this has the nasty habit of hitting walls or other object and rolling away from your target, or worse, rolling/bouncing back towards you.
Modern grenades mostly uses ball-bearings as mentioned. Another interesting development is that a Swiss company produces grenades that have an additional layer of ball bearings coated on the OUTSIDE of the grenade, and is held in place with some kind of resin. AND, they also come in mini size. So the selling point is that they are small, thus easy to carry (as well as carry more) and throw further, but still pack a hefty punch due to more ball-bearing per grenade owed to the extra layer of ball bearings.