Try getting that policy with Venice. The thing is that the landschknechts are not just cheap pikemen, they also can pillage tiles without movement cost (heal + gold) and take gold when they attack a city. With Venice's awesome gold, and the extra gold you can get from using landschneckts, you'll find that sometimes you can actually start snowballing them.
They also keep those promotions on upgrade, even though they do upgrade into the most useless unit in the game, the Lancer. It's why I mentioned Poland, since their Winger Hussar is the only Lancer unit that isn't terrible thanks to free Shock I (kept on upgrade!) and higher combat strength (plus the forced retreat thing can be hilarious at times). Sipahis are still fairly useless (the +1 movement doesn't make that much of a difference considering how weak they are anyway), especially since Landsknechts already have the free pillage promotion that Sipahis get. In the case of Hakkapeliittas, their strength bonus is essentially worthless in practice (remember that +15% strength on their 25 base strength when they are stacked with a general brings them to 28.75 strength compared to Winged Hussars' 28 base strength + free Shock promotion that also doesn't require them to be stacked on top of a unit that you'll want to keep behind the frontlines), and their movement donation bonus, while actually useful, kind of makes it pointless to keep more than 2 or 3 around depending on how many Great Generals you have, so upgrading a large army of Landsknechts into them has the same effect as upgrading into an army of Lancers.
Commerce becomes available in Medieval Era, so I see no reason why you couldn't rush that policy as soon as you get to Medieval, and make the most out of it while you can.
If you play your science game correctly, you'll enter Medieval before you finish your first policy tree, so you might not even get the chance to unlock two policies before entering the Renaissance (Rationalism!). If you sacrifice science for early culture to rush Landsknechts, then it doesn't matter how quickly you unlock Landsknechts, your (human) opponent will be knocking on your door with 6 crossbows and a knight before you can even purchase your first two Landsknechts. Most of the time (in multiplayer), Landsknechts are used as gold-purchased pikemen so that your cities can focus their hammers on crossbows and the odd knight or two. It's certainly not as bad as the non-starter Patronage policies, but it's not a stupendous bonus, either.
I've been going for DV with every civ and I'm almost done, and I think I may have used commerce instead of patronage once. I think I'll try commerce in my next game, it appears to be better than I thought.
I know Forbidden Palace doesn't matter because I usually win with 5+ votes to spare, but it will be strange to attempt a diplo victory without it.
I've also tried using Honor or Exploration in addition to Liberty/Tradition, Rationalism, and Patronage, and it makes for a longer game but it can be very fun.
Patronage policies' bonuses all seem good on paper, but prove to be inferior to Commerce in practice. For example, 25% more influence from gold gifts sounds neat, since it mean's you're essentially getting +20% gold by not having to spend as much gold to gain the same amount of CS influence, but Commerce's policies will easily get you an empire-wide +25% gold at least. City-state quests also grant you a silly amount of influence, so much so that I often don't even have to spend gold to maintain CS allies (in multiplayer). The bonus science from CS allies sounds great on paper (extra science, yay!), but in practice, the actual science amount you get is almost nothing and is easily surpassed by the science you get from gold buildings with Mercantilism. Extra happiness from gifted luxuries sounds great, except that Commerce's last policy gives the same amount of extra happiness from all luxuries, not just ones gifted by CS allies. Etc. Etc.
Honor is only really good for Warrior's Code, all the other policies' effects aren't worth it for their direct and indirect culture costs (direct culture cost from spending a policy point, indirect culture cost from increasing the culture cost of Rationalism policies and ideological tenets because of how policy costs scale with unlocked policy count). Maybe the opener is good with Raging Barbarians, but yeah, that's all I can think of.
Exploration is generally fun because it is most viable when you're running a coastal Liberty, and I find that Liberty games tend to be more fun than Tradition ones. You usually pick it up for the +Happiness from Lighthouse, Harbor, and Seaport and the flat +3 hammers on coastal cities; the opener's +1 mobility and sight on naval units is a nice bonus, but not an incredible one (it certainly becomes better if you stack it with other bonuses, like Great Lighthouse or England's UA). All the other policies in the tree are fairly terrible for the same reason as Honor's later policies: their culture cost simply isn't worth the middling-to-negligible bonuses they give. Caveat: my experience is primarily with multiplayer, so Exploration's finisher may be incredible in singleplayer, I honestly cannot tell you.
