I remember my favourite army became, Snapping Turtle I'll say. 4-6 Naginata with armour upgrades, maybe 2 yari samurai to move on the flank, and the rest archers with weapon upgrades. I could box up the entire archer host with naginata stretched way out because the enemy would be too frightened to clash with my slow moving army, or else too dead from the storm of arrows. I still remember one battle where I was worriedly facing an army with a lot of upgraded naginata cavalry on a flat map but they couldn't bring themselves to complete a charge on my shiny army and melted under the arrows. I loved how you could wipe most armies and also the challenge of attacking into trees with an army of naginata and archers which made for some tense moments, pretty sure I got wiped out once or twice trying it.
I also had fun trying an Oda army of yari ashigaru and horse archers one campaign. I decided not to attack until I had the horse archers to face the warrior monks of the Oda region so it delayed my start and eventually even gold armour ashigaru were pylons and I would have to attack armies multiple times wearing them down with bow fire, making for some frantic micro and the interesting dynamic of having to retreat and having armies that couldn't really defend.