Which minion is better to promote via Banner of Command?

If i promote a cannon minion, the tower will focus it even more, my turret damage won't be spread thus making it easy for my only strong sieger to die. But it will do damage.

If i promote a ranged minion, i'm not sure of the damage. Seems to be the safest but idk. If I was Nunu, then I'd bloodboil the heck out of that ranged minion or siege minion (idk).

If I promote a melee minion, welp turret focuses it, champions kill it first and they're the first to die. So which is a good one to promote?

So TLDR: promote who?