As far as Monarchy is concerned, I always do:
1. Manpower over Tax (Strengthen Noble Privileges). 10% tax is rarely enough to even notice an income boost, and in the few cases where your country is large enough early on to notice it, you don't need the extra 1-3 ducats anyways. 15% manpower, stacked with manpower in a lot of NI's usually removes the need to take Quantity in most cases (it's unironically one of the best government reforms around for militaristic countries).
2. Autonomy Reduction (Centralized Bureaucracy). I never really cared about this modifier... until I lived without it. Combining this with a lot of missions/events/NI's that give another -0.05 allows expansion to be consistently immediately profitable, and in addition to the new patch removing state cap, you can quickly get newly conquered land to 0% autonomy with very little effort. This is in combination with the fact that accepting cultures usually doesn't matter, and I've never needed more culture slots than the base slots + tech slots. The income boost is nonexistent, force limit, manpower, none of it really changes by accepting a culture. The only really unfortunate thing with a lot of unaccepted cultures is it being difficult to find an advisor that you can actually promote mid-late game.
3. Advisor cost, usually (Meritocratic Recruitment). This one means a little less, as the bonuses here are all pretty irrelevant. The admin one is nice if you are hunting very specific policies, but that's extremely niche. Leader cost is usually pretty bad (I guess stacking this with -50% cost from 100% professionalism is a meme?), and most countries already have Nobility as more influential than any other estate, so further buffing that is unnecessary (except as Poland, I guess?). The Burgher one is my favorite in most circumstances as stacking advisor cost, especially as you start using lvl 3-5 advisors, can save you a surprisingly massive amount of money every month. Also, loyal Burghers means even more income. Win-win.
4. Parliament or Absolutism (Parliamentarism || Royal Decree). This section feigns having lots of choices, but in truth these two are the only ones reasonable to pick in 99% of games. States General I suppose could be cool in some circumstances, or if you want to escape a terrible ruler and heir and don't care much otherwise. The 10% production is pure trash, and -0.3% army trad decay is literally unnoticeable. I've stacked to even 2-3% reduced decay and it's just such a worse modifier than yearly army tradition, don't bother with it. Parliament is great as a smaller country, and as a colonizer (there's a debate that you can get over and over that gives a colonist and faster colonies). As a rapidly expanding empire, absolutism is much better though. Once you have too much development, parliament becomes a massive hassle and you're forced to make obscene concessions to even pass one debate (you end up with many dozens if not a hundred seats, it's nuts). Another thing I can say for parliament when playing tall if that granting a province a seat gives it nice bonuses, and when almost all of your provinces have one (because they're all high dev), it's actually a noticeable increase in income.
5. Governing capacity (L'Etat c'est moi). I can't think of when this is not better, unless you're playing a tall Russia (lol?) or historical Ottomans or some country where you're just drowning in capacity. Even for a tall run like Netherlands, you run out of capacity pretty darn quickly when you're developing at kingdom/duchy rank. Even for trade companies, which are territories, you still want capacity over -10% minimum autonomy as TC's take up extra.
6. Absolutism (Political Absolutism). Another one with only one real choice, as Theocracy and Republic are pretty awful by the stage of the game that you come across this. Admin possible policies is just not even worth giving thought.
