It's always easier starting from the south I think. Satsuma, Mori and Otomo have great clan advantages, are surrounded by fertile provinces, critical resources, profitable trade nodes and multiple natural choke points.
My easiest and also among the most enjoyable campaign was when I controlled the Mori (VH/VH) and after securing a few critical provinces (for resources and choke points) and a monopoly on the trade nodes early on I was quite content to turtling down and play the trade and diplomacy game. Some overly aggressive neighbors will still get uppity but they'll usually accept a peace treaty meekly after most their armies are wiped off the map. I had no problem replacing/pumping new units since the gold flowed freely to the treasury and wako pirates are cheap as well as powerful utility unit
After a while one of my long time trade partner Hattori declared war on the Shogunate so I jumped in with an alliance offer in exchange for military access, grabbed the rich coastal provinces near Kyoto and spent a few years consolidating a foothold there. After I got filthy rich with multiple stacks of elite samurais on the field, steamroll ensued
My most brutal campaign was playing Uesugi, man I could not catch a break back then... lost count of how many times I failed that campaign before succeeding.