Crosman Valiant .177 Pellet recommendation

Thanks, WOW - There are so many different domed varieties of those brands! We did not have all this selection last time I bought pellets! The gun really slings the pellets out there so I'm guessing a bit heavier pellet might be in order. Thanks - my first post and was not sure if this would work but I'm guessing someone else has this gun and experimented with some pellets. I know of the 8 options I have in hand, only one groups nice. 
 
Scored! I found a sampler pack of pellets on Straight Shooters website and got it ordered. what a great idea for this very thing. They need to learn about USPS "if it fits it ships" because the UPS was $23.39 but they had what I needed and will look elsewhere for future orders. 

I cant wait to sight in the scope. hard to do with pellets that don't group. 

Why does the pellet make so much difference?

Thanks for your help!