Obviously, I'm not talking about Hearthfire, as that doesn't add an entire questline and stuff. ^^

But ya. Seeing as I seem to have a severe case of restartitis, I've not managed to play through the entire main quest yet with any character. I've also not played anything of the Dawnguard or Dragonborn questlines yet. But since I'm at it again (like my fourth character since I've picked up Skyrim again...) and hope to finally have found the character I will keep enjoying to play, I'm gonna ask what I've been wondering about for a long time already. I've also googled it, but didn't really find many really satisfying answers, so ya...:

At which point would you recommend playing the two dlc's Dawnguard/Dragonborn? Before or after the main quest (of the base game) is finished? I'm looking at what would make the most sense in terms of storyline (and possibly gameplay-wise too) and such. And at which character-level? Maybe add some reasoning too. I'm gonna add a poll to this thread to give me a basic overview, but I'd still like to read actual replies too.