G.B.
Any fruit they like. They all do the same thing, they provide a cold substance for the baby to suck on and chew so their gums don't hurt any more. Use any fruit you want. BUT watch out if your baby is too young. You do NOT want to add any foods to their diet until they are pretty old. I would not use fruit like this until the baby is at least 9-10 months old. They can't handle so many foods until they are older and have eaten some different foods they could be allergic to.
If they were younger then 9 months I'd just use ice in the mesh bag.