whats the easiest brain coral to keep
What type of brain coral are you looking to frag? Some like a trachaphyllia can definitely be done, but the problem is they arent a quick grower so you will have a funny shaped coral for a loooong time. However, favias, favites, platygyras, etc, all frag really easily and will quickly grow over the sides of the walls or even on the disk you attach them too. If you are looking to propagate for a little money to keep the hobby going, that would be the way to do it if you want to have a brain.
And just about all species are easy to keep.