I'd also say go for The Crown first as it's more current and the new series starts Sunday.
Also, because I've never watched downtown abbey
DEFINITELY the crown because it’s heaps better than downtown. And educational - though good to fact check things because of course it is a drama. But I learnt some really interesting stuff, like the story of Churchill and that painting, or how close the Duke of Windsor’s connection to the Nazis was...
It is amazing how good the show is at making you pity those in a life of extreme privilege and wealth.
Margaret’s story is especially well done, because they do show her being a brat and a snob but her fate still feels tragic. No doubt about to be even sadder this series, her husband was a total bully in real life (is it shallow to say I’m glad they’ve changed actors because I really fancied him and wouldn’t want to watch that). I will miss Vanessa Kirby, however famous Helena bonham Carter is, the jury is out for me on whether she will be as good.
But thank goodness for Olivia Colman, I don’t think any safer hands could take over. It will still be strange to adjust to though.