I've owned 10 or 12 Glocks and in my experience they either fit your hand or they don't.
The finger grooves feel good or they are a nuisance. But also the hump on the backstrap fits some hands better than others, and it's in a slightly different location depending on the model. I have really big hands with long, skinny fingers and the G19 actually fills out my palm better. The finger grooves aren't well aligned for my skinny fingers though, so I have tried many different grip sleeves over the years. I ended up settling with the Pachmayr one, which fattens the grip over all (for my long fingers), virtually eliminates the finger grooves (so my skinny fingers aren't forcefully separated) and the G19 hump is still in the right place for me.
TLDR version: handle as many as you can, keeping in mind what a grip sleeve or tape may improve, and buy the one that feels "right."
The finger grooves feel good or they are a nuisance. But also the hump on the backstrap fits some hands better than others, and it's in a slightly different location depending on the model. I have really big hands with long, skinny fingers and the G19 actually fills out my palm better. The finger grooves aren't well aligned for my skinny fingers though, so I have tried many different grip sleeves over the years. I ended up settling with the Pachmayr one, which fattens the grip over all (for my long fingers), virtually eliminates the finger grooves (so my skinny fingers aren't forcefully separated) and the G19 hump is still in the right place for me.
TLDR version: handle as many as you can, keeping in mind what a grip sleeve or tape may improve, and buy the one that feels "right."