And there are plenty of discussions online for pretty much every card on how strong or weak people think the cards are overall (like is it worth picking it up if it's offered to you late in a run because the payoff might not be worth it, or if you see you're getting a specific boss that act, etc), and most of the cards have been buffed or nerfed multiple times since the game has come out, so clearly the developers have been convinced that some strong may end up stronger than others on average too (and are trying to keep things pretty even as much as possible, I assume).
With that said, as the Defect, Defragment and Capacitor are nearly always a no-brainer. Capacitor not so much in Act1, because nothing lasts long enough for it to pay off. And if you've got anything that adds orb slots, Consume becomes really powerful (even without, you can do 10 damage a turn from two orb slots instead of 9 from three, which isn't nothing).
Loop builds are very strong as well, but trickier to get right because you need to pay close attention to your front orb. Finally focus+frost can easily give you so much block most enemies can't cut through. (Watch out for Reptomancer, though, she doesn't respect anyone without DPS.)
But I was a little too weak on my defense that go (had some frost generation, but not enough), and I made a dumb mistake attacking the Masked Bandits instead of losing all my gold, who did 50 damage to me before I killed them, bringing me down to 18 health, then I couldn't get to a campfire until I fought 3 more regular enemies, and the next enemy brought me down 6 more, then the second enemy after that got me down the other 12. Oops.
I'm a bit tapped out at A8, but it's amazing how the base game goes from nailbitingly impossible to seeming pretty straightforward. (The mechanics contribute to this: the easier a battle is, the more upgrades you do and the more likely you are to grab an elite relic.)
Good luck with Watcher. The biggest advice here is: play it safe until you have multiple cards to get out of wrath. Watcher is super-powerful and _very_ easy to mess up.
For the ironclad, you might take a cleave, or a whirlwind, or a spot weakness, or an inflame in act 1. The first two give you AOE, and the last two will help scale damage if you find a limit later on.
I mean, that is perhaps part of your problem. There aren't any cards I've not picked at least once and made good use of on ironclad even at A20.
The game really is more about building a deck based upon what comes up and constantly reassessing what is actually working in your current deck.
Choosing "good" cards based on their overall strength out of context is essentially a brute force approach to winning.