Is there any fish with better oils than others and less bones ect ...
Just as a treat so not an everyday thing.
Sardines; tuna they love 'em!
Assuming you are considering fish cat foods, such as salmon, shrimp, whitefish, tuna, etc., Then the amount of actual fish is not really that high. There will be a lot of fish by-products, and even meat by-products. And little bits of bone is actually calcium, so not a real concern assuming they aren't of any noticeable size.
But if you are looking for a fish treat, it is hard to beat bonito fish flakes. Cats go crazy over it, and a little goes a long way. I have provided a link to one brand.
TUNA, depends if the cats a good eater
