Whichever tube you can get that would be the most perpendicular to the shock mount would (theoretically) be the best. Your shock is pushing mainly upwards, with a bit of the force going inwards towards the center of the truck. That bit of inward force x the length of the shock tower is going to be equal to the torque that's being applied to the frame rail. If you can have a force (compression or tension) that is as perpendicular to the shock towers as possible, that would be best. The force the shocks are applying perpendicularly to the tower isn't greater than the max force a tube can apply in either tension or compression, so I don't think that's something I'd be worried about. I think the tube going into the center would be better for cancelling out forces as a whole, but running a tube from the top of the tower towards the outside of the vehicle would work just as well.