How do I get podcasts downloaded directly to my iPhone and iPad to match the ones on my Mac?

You say that sometimes you "forget" to sync. Are you utilizing Wi-Fi syncing? The sync activates whenever you're on the same network and your device is plugged in. This might reduce the number of instances that you need to download a copy from your iPhone.

I realize this is a stop gap. I feel your pain. Like you, I've put a lot of effort into understanding why the leading podcast catcher can't seem to make podcasting on the iOS "just work". In the end I needed a bit of self inflicted tough-love and just admitted that this was one are that Apple fell short and that they weren't going to remedy anytime soon. They're putting their resources where the revenue streams are.

My situation forced me to change my workflow. I've been waiting for the promise an untethered world, and jumped into iCloud full steam. I use iTunes Match for my music, iCloud for my backups and no longer sync to iTunes on my computer. Of course, this means that there is no way to subscribe to podcasts on my iPhone without using a third party app.

After trying several podcast apps, I've come to like both Downcaster and Instacast. I've imported my feeds from my mac, I can subscribe to new ones on the iPhone, and I can sync to my other devices through iCloud. What I can't do is sync back to the mac. But I'm ok with that now. By using a full featured app on the iPhone, I've come to really like the experience. Given the choice today, I'd continue my new habit of listening to podcasts on my phone even while I'm working on my mac. I don't ever need iTunes open and the overall listening experience is much better.

I suspect you have somehow added two slightly different feed sources - one on the mac and one on the phone. Delete all episodes of the podcast from both places and start over with just a single subscription initiated in iTunes on the Mac.

Here's how I went about testing my idea about feed sources being the issue:

I just "subscribed" to Marketplace by manually downloading the same episode on both my phone and my Mac without having any pre-existing subscription on either.

When I synced (WiFi?), I did not end up with a duplicate episode.

Then, to try to break things, I also tried downloading an episode on the phone and syncing it to the Mac once the download completed. I am not able to reproduce the problem you describe with artwork/title mismatch.