It's not about pixel density, it's about pixel density AND screen size...retina means you can't see individual pixels. The PPI that achieves that differs based on screen size, simply because larger screen = longer viewing distance. I'd imagine the iPad is borderline retina display since you use it at table distance, not 6" like with a phone
That being said, I'm not obsessed with the iPhone enough to try and say retina > samoled. I have a Samsung focus, which has the same samoled screen as the galaxy s (or is it amoled...I'm not sure). It's beautiful, but the only real advantage I actually see in day to day use is the quality of the blacks...and colors do pop better, but thats especially noticeable with windows phone 7. I don't think it'd matter as much with how iOS is designed.
Of course, in my opinion the advantage with the iPhone screen comes not so much with the pixel density, but the fact that the screen is laminated directly onto the glass...it makes the screen appear painted onto the glass, not as if it's sitting behind the glass on other phones. It's a great aesthetic