Both rifles are about the same in price. The 880 is about $5 more than the 764.
The 880 has a 50 round capacity. The 764 has an 18 round capacity. The 880 has a rifled barrel, the 764 has a smooth bore barrel. The 880 is rated at 750 FPS, the 764 is rated at 625 FPS.
If it were me I would select the 880 over the 764
It's a Crosman 764sb air rifle.
It's a fine inexpensive rifle for youth. It is designed for learning how to handle a rifle safely and for plinking at targets. It is not a hunting or competition rifle, but is designed for fun.
The model 760 is Crosman's version of the Daisy Red Ryder. There are so many versions that it would be a full time job trying to collect all the version's. (Example) The first one was the Canada boy (1964), then 760 powermaster, 760/20, 760XL powermaster, 760AB, 760B, 760BRD, 760P, 760SK, 760XLS, 760 40th, 761XL, 764SB, 766 American classic (this last one is the nicest of all of them). They started the model in 1964 and are still made today. The 760B started production in 1997 along with the 760AB at the same time. but the 760AB was discontinued shortly afterwards. probably because it used a .175 caliber BB not the more popular .177 BB. My guess is the model 760C came out sometime after 1997. I don't have all the variations listed here so I'm providing a link to All of Crosman's owners and parts rifle models. Take a look at the 760 section and you will get an idea of how complicated is gets trying to follow this model (See the link Below)