Of the four most popular British female singers in the 1960s, only Dusty and Petula had significant success in the US, the best test of an artist. Their singing ability was head and shoulders above that of Ciila and Lulu.
Cilla's big advantage was that she had a great record producer in George Martin and some good songs, although some were cover versions on American hits. Her version of the Righteous Brothers' You Lost That Lovin' Feeling was very inferior to theirs. Luckily the record buying public realised it too.
Arguably Cilla had greater success as a TV personality than as a singer.
I don't like Dusty's voice that much and prefer Cilla's, when she was at the top of her game (pre nose-job). That's my preference but thanks for your response anyway.
For me Cilla's version of "I've been wrong before" is miles ahead of Dusty's for example. You will disagree, as will most others but that's fine.