The larger, more national/international a charity is, the more overhead it costs, in general.
There are sites that attempt to give quality ratings to charities, and the US based ones at least have to give some data to the government if they want to be included in federal employee charitable giving (though the process is, in and of itself, a bit of a scam).
If you have heard of a charity or seen an ad for it, chances are it has a significant overhead. If its a 'famous' charity, then it has a MASSIVE overhead. If it is for a trendy cause, almost guaranteed to be a 90% overhead scam. For sure all the "Give to Jamaica!" things you are about to see after the hurricane are scams where the $100 you give will end with a $1 bottle of water showing up in Jamaica. An established, long running emergency response or medical aid org at least will probably deliver ~50% of the money given in the form of on-the-ground aid, which for an off shore island in a disaster, is probably pretty reasonable given the logistics. But lots will sub-contract to folks who sub-contract to folks who sub-contract and all those middle-men take their cut.
So give to a church if you want, where you can SEE the end result, or just to support the PR campaign of a charity that sponsors a cause you align with. There are a few folks that might serve to vet small, largely unknown, charitable groups, but otherwise its a total crap shoot.
As mentioned above, go donate blood if you are eligible, or at least donate $$$ to your local blood donation service. That is, BY FAR, the largest bang for your buck "my time/money equals lives saved" thing any normal person could ever do.