Let me play devil's advocate for oligarchy. I used to consider it the strongest for of government for a long time, granted that was in earlier patches. But still I feel some of things that made it good once are still true and so I think I can try to highlight some of it's advantages.
Oligarchy has agendas and the ability to change rulers when it still matters. With dictatorship or imperial you're just shit out of luck if you roll a bad agenda and / or ruler because you'll never change your leader in time for it to be relevant. And democracy just doesn't have agenda's at all. Also imperial was always terrible for as long as I remember. And probably still is but to be fair I think the last time I played a full imperial run must've been 1.5 or something.
Now, as I already mentioned, I considered oligarchy to be a lot better back when you didn't need influence for everything. Can't really pay 200 every 20 years in 2.1, at best you'll do it once or twice, if it really matters and you happen to have it. But even if you never use that option and always random between all candidates it's actually okay. Dictatorship is like oligarchy's high risk high reward option. With oligarchy, if your current ruler is great they'll probably be replaced with someone more mediocre in 20 years. And they are terrible then the same happens. Tends to average out to "okay".
There's an argument to be made for sacrificing your chance at 80 years of great rulers for avoiding 80 years of terrible rulers. It probably depends on the specifics but that's a trade off that can be worth it in my mind. Oh, and If, for some reason, you were swimming in influence then oligarchy is pretty great. But also I don't know why you would ever be swimming in influence in 2.0+
