Can't forget about the Soviets and Afghanistan. With a far greater military force (in numbers and equipment) they were hopelessly bogged down. I don't care how many wealthy folks/sick bastards the enemy has bankrolling them. They are hopelessly outgunned and outmanned (in the senses of ability, technology and training.) They are fighting with 20+ year-old equipment. And they are not benefiting from quality intelligence and information about their enemy, such as the Mujahadeen did in the 80's.
They do have some advantages. Like the Viet Cong, they have the lay of the land. They have some local populations that are sympathetic or terrified collaborators. They have an unstable political and social situation to exploit. And they are ruthless, conscienceless animals.
Don't get me wrong. They will do some damage. Those 20+ year-old weapons can still kill. But this is a war, isn't it? War is never pretty or neat. But it is sometimes necessary. I think most of us will agree that this one is.
But we've learned a lot from Viet Nam. And the Soviet disaster in Afganistan. I would say the smart money's on us.
P.S. I'd like to see some more of out troops in there, too.