Like Timberstalker said its a lot of personal preference. .29 is large, covers a lot of your target especially at longer distances but the larger pin/fiberoptic will gather more light. .10 is smaller, "could" allow you to be more precise but it gathers much less light so the pin itself can be harder to see in low light. I've played around with all of them and prefer the .19, seems to be a good happy medium for me.