Pitch shifting/stretching algorithms' comparison

“I've had much better results with Izotope RX than Studio One for example for stretching.”

Also, Bitwig can be good.

You can also try out paid Lossless Pitch AI on dango.ai (tuanziai.com/en-US).

or paulstretch

“if you want to retain the original pitch this is the first tool that comes to mind”

Kairos on UVROnline.app (the pitch button in the audio editor there) gives much better results than Izotope RX (more).