Quick note to the mentions of nurgle bikers and spawn. It's a juggerlord. He's khorny. No nurgle here, saddly.
As to my input, bikes everyday. Bikes have the mobility technique described above, you can get actual weapons on them, and random firepower won't completely erase your spawn. What you get is firepower ahead of your charge, you still have two attacks a model, 3 on charge, 4 with khorne along with a re roll charge range banner (you never know) a static cover save for when ap 3/2 starts shooting at you, options for plasma and melta so you can thin a 2+squad down before going in a bit. You also have a character that can take the challenge that WILL be issued, so you have the choice depending on the unit.