In Magna Mundi, it's not an oxymoron. The AI is improved to be smart enough to realize that going to war with a member state of the Holy Roman Empire is asking for major pain, as the Emperor will usually join to aid the attacked member. Upon that, even if you do get territory taken from you, the Emperor will apply pressure to get the province returned to it's rightful owner. Or the Imperial Demesne. Really depends on the selfishness of the emperor.
I have a few go-to states in Magna Mundi that I enjoy greatly.
Bohemia is great, especially if you give in to the Hussites.
Venice is amazing if you want to focus on expanding your trade empire more than your military might.
Burgundy has a method to it that gets you on the fast-track to becoming Holy Roman Emperor, and subsequently, a kingdom. At the beginning, in 1453 anyway, Burgundy will get events to simulate the French/Imperial partition that came from the Bugundian Succession that divided it's territory between the Holy Roman Emperor, Austria in real life, and France, The Dutch and French parts going to Austria and France respectively.
However, if you add Burgundy's non-imperial territory to the Empire to improve relations, you can officially join the empire, and win the title of Emperor, which will allow you to elevate the Burgundian Crown to the Kingdom level, co-equal to that of the Kingdom of France, which prevents the Burgundian Succession, for one thing, and elevates Burgundy to Kingdom Tier. Burgundy is extremely powerful, with most of the extremely rich and populous Netherlands, Dutch as an Accepted Culture, and some of the best national ideas to fast-track it to Scientific Revolution and Liberte, Fraternite, Egalite. In otherwords, it can very quickly rise to superpower levels of awesome. If you're careful.
Transoxiana -> Mughal Empire. Nuff said.
Any Japanese minor is fun too.