I agree that Steelix isn't the greatest, though I've had better luck in battle with ones that have an adamant, brave, careful, or sassy nature.
Adamant ups attack, lowers special attack
Brave ups attack, lowers speed
Careful ups special defense, lowers special attack
Sassy ups special defense, lowers speed
I find these natures the best because Steelix's special attack and speed are already awful anyway.