I've never been a major Madonna fan. In my mind, she's more of an interesting personality rather than a terribly good singer or actress. As a singer, I enjoy songs like "Material Girl", "Like a Prayer", and a few others, but overall, I don't find her to be a good singer. As an actress, she's probably one of the worst examples of a pop singer trying to find validation on the big screen. Her leading roles in the eighties, such as SHANGHAI EXPRESS and WHO'S THAT GIRL, are laughingly bad, but she kept on trying. THE NEXT BEST THING is one of the worst movies I've had the misfortune to see. Yes, it was that bad. Madonna was only good in A LEAGUE OF THEIR OWN, and that was only because she wasn't the main character. She probably does better in smaller, supporting roles, but even those might be too much of a stretch for her.
Barbra Streisand is a good example of a singer-actress, even though I'm not too fond of her singing necessarily. She has a pretty voice, sure, but it's the style of music she sings that I don't generally care for. Streisand is a beautiful woman, especially in her prime, and I think she deserved her Oscar for FUNNY GIRL, her highly heralded film debut. I remember watching HELLO DOLLY years ago and enjoying it. I also liked FOR PETE'S SAKE and THE MAIN EVENT, the latter being perhaps my favorite of her movies. A STAR IS BORN is probably one of her more popular movies, and it's enjoyable too. The one thing that always disappoints me about Streisand's movies is the language in them. They swear too much and I don't watch them a lot because of it.
Dolly Parton falls somewhere Madonna and Barbara Streisand. She is certainly a more capable actress than Madonna, but she doesn't quite have the prestige of Barbara Streisand. For example, Dolly shows easy on-screen charisma in movies like NINE TO FIVE, but she never had a big production like YENTL to add to her resume. Whether or not you consider Dolly a good actress will depend on your perspective. She's beautiful and likable, but all of her roles seem tailor-made for her. There isn't a whole lot of acting required; she's always Dolly with a different name. Her screen presence is that major redeeming factor for her apparent lack of acting versatility.
One of the best examples of an actress-singer is Cher. Not only was she a part of Sonny & Cher, one of the more popular duos of the late sixties, she also transitioned easily to television with THE SONNY & CHER SHOW in the seventies, where she showed considerable comedic talent. She got more serious about acting in the eighties and she turned in solid performances in COME BACK TO THE FIVE AND DIME, JIMMY DEAN, JIMMY and SILKWOOD, the latter receiving her critical acclaim. Cher felt robbed, and perhaps rightfully so, that she wasn't nominated for MASK, one of her finest performances, but she won the Oscar for MOONSTRUCK, one of my favorite romantic comedies. She also had good performances in SUSPECT and MERMAIDS, but her film career was short-lived. She turned back to music in the late eighties and she's made few movies since.