Steelix by yourself is a pretty cool pokemon, and it's a great addon to Onix. The mega is pretty forgettable... But it does the job. However, most of the time I forget it even exists.
Gallade is really cool, and imo, it's better than Gardevoir. It does the knight thing really well and looks like a capable ally or hero. Mega Gallade doesn't add much, but making the blades longer and adding the cape really adds to the hero effect.