What is your favorite Powell/Loy film?
The Thin Man (which, along with Bringing Up Baby, holds the title as my favorite film, period). I watch all six of the films in that franchise with some regularity, especially the early ones, which are superior. There are a couple of things from the novel I wish were in the film, and one thing from the Lux radio adaptation, but it's something close to perfect as it is.
A close second is Libeled Lady. I'm not a huge fan of Jean Harlow - I don't dislike her, but a little of her goes a long way for me. With a foursome cast, it's the perfect amount. I do wonder if this film could have been even better had Clark Gable been cast as originally planned - since he works so well with all three costars - but Spencer Tracy does a great job. Walter Connolly is a delight. And the Loy/Powell combination is winning as always. I love the evolution of Bill and Connie's relationship; how she has his number at first, how their feelings for each other change (as a side note, I'd pay big money to see the deleted scene from the first night at the cabin), and how lovely and natural they are together as a couple. I also adore that his revelation of what was originally planned happens off-screen and is not something she has a fit over. Katharine Hepburn called this film "the funniest damn thing I've ever seen," and I can't argue with her.
I also adore Love Crazy and I Love You Again. Jack Carson is a wonderful addition to the former, and Frank McHugh to the latter. Loy dumping a plate of scrambled eggs on Powell's head never gets old.
Their first collaboration, Manhattan Melodrama, is a good showcase for Loy, Powell, and Gable. All work nicely together (it's no surprise to me that Loy starred with Gable numerous times as well, although nothing close to her 14 collaborations - well, 13 plus a cameo - with Powell), and I really get invested in the characters. I wish Evelyn Prentice had been a better script and thus a better finished product, as I'd have liked to see them continue to do dramas together as well.
Double Wedding, as has been discussed elsewhere on these boards, has a bit of an off feel to it, but still contains quite charming moments (e.g. the picnic, the early scenes in the trailer). Jean Harlow's death in the midst of production plays an obvious role (she was Powell's girlfriend and Loy's friend), but the script also kind of falls apart in the end and the slapstick isn't really their bag.
I don't watch The Great Ziegfeld very often. They do a good job as always, but it's such a whitewashed version of Flo, and of Flo and Billie, that I can't really get into it.
All in all, I'm pretty sure I'd watch Myrna Loy and William Powell read the phone book. Their real-life friendship was really something special, and they absolutely loved working together. That goes a long way.