How much you like or dislike the user interface of any program depends on a lot of factors like how well you know the program, the computer and monitor you use, and how you use the program. The combination of those factors and many others affect your opinion of a UI. I prefer to keep things as simple as possible. For me, Lightroom is much easier to deal with and I don't think anyone would argue that it's more intuitive to use than Aperture. I've never had to refer to the user manual as much as I did with Aperture this past week. I also watched the instructional videos on Apple's website. The Aperture user manual is almost 500 pages long! That alone should tell you something about its complexity. Remember, when Lightroom first became available as a public Beta, there was no user manual. We were left to figure it out on our own and it wasn't difficult. That says a lot to me about just how good the user interface is in Lightroom.
I don't want to sound like I'm bashing Aperture here. Given the right conditions as discussed above, this program really cranks. Having a large monitor is key for using Aperture and dual monitors is even better. A fast computer with a lot of RAM is also important for Aperture. I like the floating HUD displays and the full frame mode but I don't like the way the HUD covers up my images which, again, wouldn't be an issue with dual monitors.
The Loupe tool in Aperture is by far one of the coolest tools in any image management software anywhere. I love that I can loupe an image anywhere in the interface on the fly. Sadly, the zoom tool isn't quite as nice and scrolling around a zoomed-in image is a nightmare in Aperture. When I first started using Lightroom, I didn't like the zoom feature all that much and wished it had a loupe tool like Aperture. But now that I've worked with it a bit, I prefer it, especially for checking sharpness. I can zoom to 1:1 and scroll through all of the images super fast with the arrow keys.
Aperture also has the light table mode which is completely different than anything in Lightroom. It seems pretty nice but I don't exactly know when I'd need it.
Overall, the simplicity of Lightroom allows me to concentrate on the image more so than in Aperture. It shouldn't be about the interface--it should be about the images we're working on. And that pretty much sums up the user interface debate for me.
Developing Images and Image Quality
I realize that what I'm about to say is akin to sticking my head in the Lion's mouth. I just finished a head-to-head comparison of Aperture's adjustment HUD versus Lightroom's develop module, and I exported the images and compared them in Photoshop CS2. I also made my image adjustments individually in each program. This isn't so much a comparison of how the images look side by side, but how the process went and the final image "quality."
I started with Aperture and worked up one image from a recent stock shoot of some cowboys. After wrestling with the user interface for several minutes, I came to grips with the fact that I couldn't get the bottom image browser to go away so that I could have my image and the Adjustment panel side by side (see image above). Maybe there's a way to do it, maybe not. (I'm sure I'll hear about it soon in the comments.)
Apertures HUD controls seem to work very well once you get used to them. I struggled with not being able to use the option key with the exposure slider to judge when the highlights would blowout, but I soon found the familiar highlight warning that allowed me to see when I had recovered all the highlights. Please note that I decided to not apply sharpening to any of the images I processed for this comparison so that I would be comparing apples to apples in the image quality comparison.
As I wrote last week and above, I'm not blown away by Aperture's user interface. Even in full screen mode, the image was covered by the HUD (see image below), and its hard to see if there are parts of the image that are blown out with it covered up. Hence, my previous comments on Aperture being suited to dual monitors where you can have your image on one Monitor and the adjustment HUDs on the other. Anyway, back to the images.
The next step was to work up the same image in Lightroom. And refreshingly, I could concentrate on the image and not the interface (see image below). No hunting for drop-down menus or keyboard shortcuts to alter the user interface. In Lightroom, you just click the triangles and the panels go away.
Lightroom Version 1.0 now has these amazing new tools called Targeted Adjustment Tools that allow you to click the tool and take it into your image to make adjustments directly on the image. These Targeted Adjustment tools exist for the Tone Curve, HSL, and Grayscale palettes in the Develop Module. Check them out if you haven't already. They're really intuitive to use! Aperture has nothing like them.
I also find the layout of the develop tools much more logical in Lightroom than in Aperture. In Lightroom, it's logical to work your way down the sliders since they're laid out that way. In Aperture, I found myself skipping all over the place, starting with recovering highlights, then white balance, etc. Maybe that's because I don't know the program as well but I'm sure it's also from my old habits with ACR.