At first thought, they're radically different. The Banshee is an all-around solid jack, while the Hydra is oriented towards shooting.
But when you break things down, you're looking at (strictly shooting), a loss of 3" and 1 POW. That's it. Depending on the board, that might let you aim for RAT7, but it's hardly enough to balance out the numerous advantages of the Banshee - foremost that it causes KD, a great buff in our faction of average accuracy and lacking DEF debuffs.
Of course, Wailing, fantastic melee (Reach PS17) doesn't hurt either. Chain G&S doesn't put Hydra's melee ability anywhere near Banshee's.
The loss of 1 SPD is not meaningful at all in this comparison, as the Hydra almost never wants to close. Finally, the Force Cannon on the Banshee can't be destroyed, another huge advantage, as once the Hydra starts taking damage, the generator is placed pretty high up on the grid.
I'm thinking that people generally feel the same way, but does anyone disagree / want to play devil's advocate? Been looking at the Hydra for some test lists, and unless Banshee doesn't release by end of 2013, I don't really see any reason to take Hydra any more.