Right around Season 3. Seasons 4 & 5 contain the bulk of the decent arcs. There's one or two of them in Season 2.
You kinda have to cherrypick with that show. I can't imagine actually watching all of the episodes, in order, all the way through. Lotta episodes I got 3 minutes in and was like "nope"
Agree 100%. Show picks up major steam half way through Season 3 (you can literally
see when the change happens because the graphics quality is suddenly upped and Ahsoka/Anakin/Obiwan all look way more mature), but even that was really just going from a minority of episodes per season being worth watching to a majority per season, there were still some god awful arcs right up to the end.
"Heroes on Both Sides" is the first episode released after the quality is upped. Good episode too, I suggest people just start with that or Mortis. Somewhat ironic, but just, the episode before it was the last episode Ziro was in, aka the Jar Jar of the Clone Wars. Unless you want to slice off some cheese and have a laugh at one of the lowest lows of Star Wars, don't watch any episode with Ziro in it.
Watch all the episodes featuring clones as the focus
Ehhhh. Some are okay, some are awful, and they were a bigger focus in the early seasons which even the best of are crap compared to later seasons. IMO the consistently good arcs, at least in the second half of the series, were the Sith focused ones. (IE Ventress, Savage, Maul) But Anakin and Ahsoka arcs are also mostly great too, in fact really in the second half of the series you only need avoid the droid and "youngling" arcs.