It's tough to say without having them to compare. I think you have to look beyond just screen resolution though, and figure out which product has the best all around feature set and apps. Screen quality is very important, but it's not enough to make a purchasing decision, as there are so many other things that also add value.
I don’t know for sure if it is THE best (which is both subjective and objective to a degree), but the new Nexus 7 is pretty close. The Nexus 7 screen’s dpi is higher than a iPad’s Retina display. The Kindle Fire HD also has a nice screen.
Screen quality for tablets has improved greatly over the past year, and devices such as Google's Nexus 10 and the Sony Xperia Tablet Z sport razor-sharp screens. Google's new Nexus 7 also has a great screen. But I'm not sure any of them have surpassed the fourth-generation iPad. I think you'd have to do a side-by-side comparison to render a judgment.