Both of these are great films noir, or film noirs, however you'd like to say it. They're both great. If you like old black and white movies, gritty and full of crime, you'll enjoy either of these.
Murder, My Sweet is an adaptation of Raymond Chandler's novel, Farewell, My Lovely, with Dick Powell as detective Phillip Marlowe. The movie takes place almost entirely at night in L.A., which gives it this strange, dreamy quality that borders on nightmare at times. The dialogue sounds a bit dated sometimes, but you get blackmail, a femme fatale, and some wonderful costumes, not to mention a very strange drug-enduced hallucination sequence. I'm not a big fan of Dick Powell, and thought he was kind of an odd choice to play Marlowe. Let me know what you think.
Where the Sidewalk Ends has nothing at all to do with the children's poetry book by Shel Silverstein. I'd never heard of this movie, but it is a wonderful little thing, with a great noir hero/anti-hero in Dana Andrews as the hard boiled cop with a troubled past. His face is just so great under the brim of a fedora. Lots of smoking, drinking, and punching in the face. Co-starring the lovely but rather flat Gene Tierney, with a cameo by her husband of the time, Oleg Cassini as a clothing designer (what a stretch!). Whereas Murder, My Sweet is quintessentially Los Angeles, Where the Sidewalk Ends is utterly New York. It's grim, murky and beautifully directed by Otto Preminger. Of the two movies, I prefer this one.
As far as the costumes, both films offer up great fashion. I always wear a sequin-encrusted full length evening gown to go see my favorite private eye, don't you? And it's always two o'clock in the morning. Plus, you can see where so many of the standard plot points in movies today got their start.
"You look all bunged up like a barrelhouse vag." You just don't get lines like that anymore.