Starting with the easiest, assuming you do the "ideal" strategy:

Hojo
Uesugi
Takeda

Shimazu
Imagawa

Oda
Mori

The takeda, hojo, and uesugi campaigns are the same after the first 5 years. If you start as takeda, you wipe out the hojo and then the uesugi. If you start as the hojo you take out the Uesugi. If you start as the uesugi you take out the hojo. Anyway you slice it you end up with a ton of money and a narrow front to attack.

Shimazu and imagawa are basically the same, conquer kyushu then expand.

Mori and Oda, whenever I played them I would conquer the center of the map, then get the urge to tech up for a couple decades. Then I would fight one battle with my muskets/heavy cavalry/honor 5 monks or whatever, get bored, and geisha the rest of the clans.

I think the only campaign I ever lost was as Oda, back on old shogun. I took the middle 10 or so provinces and sat and waited for the hojo horde. Got both a shimazu horde and a hojo horde, then shimazu got assassinated and left all his men to hojo. Then my daimyo got assassinated