Tricky.
Well, I haven't seen Endless Odyssey, so out of the remaing three, I'd rate them in this order: Galaxy Railways, Maetel Legend and Harlock Saga. I didn't think Harlock Saga was very good at all, so I'd suggest you rent that one before or instead of buying it.
A few other titles come to mind, though: Gun Frontier, Cosmo Warrior Zero, Queen Emeraldas, and Interstella 5555.
Those that I'd consider good are Interstella 5555, Gun Frontier, and Galaxy Railways.
Those I'd consider average are: Cosmo Warrior Zero, Maetel Legend, and Queen Emeraldas (the first two eps, anyways).