BlitzMax doesn't have the same ease of use as Blitz3D but does offer multi-platform.
I'd say that's very much dependent on where you came from, if you're new to programming, B3D isn't going to be any easier to learn, some of the things I found confusing at first and I'd programmed in other languages prior to it.
I'd say that neither are hard to learn, but BMax is probably harder to master (since there's a lot more you can do with it).