For those who don't care to read the minutiae, I'll get to the point: In my opinion, Aperture vs. Lightroom is the same discussion as Canon vs. Nikon. Each has strengths and weaknesses, but it's not a no-brainer decision either way. You'll produce good results with both applications, and the real decisions come down to personal preference, and specific features that you may need for a very specific reason.
So, let's dig in deeper:
It may seem shallow to discuss each app's visual appearance, but it's the first thing that hits you when you launch them and, when you're going to live with one of these apps for some time, you don't want to hate it every day.
Coming from Aperture, where everything is a lightish shade of grey, Lightroom's UI two-tone palette of black and quite dark grey feels really heavy. It reminds me, really, of the Disaster Area stunt ship control panel from Hitchhiker's Guide:
When you press the black button labelled in black on a black background, a black light lights up black to let you know you've done it!
I don't like the look of Lightroom, but I could get past it if I had to.
Although better than some other applications that Adobe have produced over the years, Lightroom just doesn't feel totally like a Mac application to me. In particular, the fact that the Library navigator panel has a scroll bar on the left-hand side of its view really makes my skin crawl. A small detail, granted, but I do notice these things.
Another thing I don't like about Lightroom is the use of plain text labels as buttons in the "Fit, Fill, 1:1, 1:2" options in the Navigator panel, as well as the large "Library | Develop | Slideshow" etc. at the top-right.
My last general gripe about the Lightroom UI is the light watermark it puts on the grid view with a large number behind each thumbnail. Again, it's a sufficiently close shade of grey to the thumbnail background that it's hard to read, unless you look intently at it. When the thumbnails are small, it just looks like visual noise. Not only that but, if you flag an image, the flag icon is drawn over the top of the number - more noise. Perhaps I haven't appreciated the point of them being there at all.
One very nice feature in Lightroom, though, is the small HUD window that pops up with the name of the command you just invoked with a keyboard shortcut. Really helps learnability and increased my confidence a lot.
Lightroom has some serious strengths here. I absolutely love the Metadata Browser - when you want to search by some photographic attribute, this beats the pants off setting up a Smart Album or configuring the query HUD in Aperture for speed of setting up the query and for speed of getting the result. It's like lightning.
However, I much prefer the uncluttered arrangement of Aperture's projects panel - it's just all my 'photo containers' and isn't mixed up with search and metadata.
I don't use Aperture's referenced masters feature - I like to keep all my masters in the Aperture library. I feel the UI to this functionality is much better in Aperture than in Lightroom. When I look at Lightroom's import panel, I feel a bit intimidated and don't quite feel confident that it's doing what I want it to.
Applying ratings is one of the most important parts of a post-shoot workflow. Lightroom differs from Aperture in the ways that you can rate images: in Aperture you have a simple range from -1 (called "reject", but it's treated as an ordinal value one increment below zero) through to 5. In Lightroom, you have zero through five stars, plus three flag states: Pick, Flagged, Reject. This means, oddly, that an image can be a five-star reject or a zero-star pick.
I do like the provision of an out-of-band 'flag' in Lightroom. The ability to mark an image as needing attention without having to override the semantics of a particular star value is useful. I often rate a shoot and want to mark the ones that I think don't work in colour, but might in black and white. The Lightroom flag would be great for this.
In Aperture, you have keyboard shortcuts to filter any thumbnail view by star rating: ctrl-` for Unrated and Better; ctrl-1 through ctrl-5 for "X stars or better", ctrl-6 for all images; ctrl-7 for unrated images and ctrl-8 for rejects. I find it strange that Lightroom doesn't provide keyboard shortcuts for this, as I use these keystrokes as one of the main ways to filter through a large project or album of rated images.
I adore the interactive histogram in Lightroom. It's a fantastic bit of UI. The Tone Curve is far more intelligible than Aperture's Levels adjustment.
However, I found Lightroom's little on/off light switches to be unintuitive as a way to enable or disable the adjustment. What would have been so wrong with a checkbox? Also, it was not at all obvious that double-clicking on a slider would reset it to zero, although this does provide the ability to reset a single slider within a control. In Aperture, you can only reset the entire adjustment.
I really, really, really like Lightroom's Split Toning control. Really really really like it. I haven't played with the Lens Corrections adjustment yet.
Are Lightroom's adjustments better than Aperture's? I haven't put enough images through it yet, but my feeling is that Lightroom has some tools which Aperture doesn't have (Split Toning, Presence, Lens Corrections) but I'm not seeing a huge difference between the adjustments which they have in common.
I'm also unable to detect a significant improvement in Lightroom's default RAW decode from Aperture's on my Canon 30D RAW files.
The major stumbling block for me in thinking about adopting Lightroom is that Aperture has a far stronger export workflow. In particular, ahem, in sending images to Flickr. Given that the vast majority of my images only ever appear on Flickr, being able to get photos simply on to Flickr is critical for me.
Aperture gives Lightroom a good kicking here.
Aperture has superb support for dual displays. I haven't tried Lightroom on a dual display setup, but I typically use Aperture in second-display 'alternate' mode which shows the currently selected thumbnail in full-screen on the system's alternate display. Perhaps someone can enlighten me in the comments on what Lightroom offers in this area.
Performance is a feature. Lightroom takes Aperture around the back and delivers a trousers-down six-of-the-best spanking in performance. Lightroom screams, but it gives up a smidgen of polish to do so.
In particular, when you're applying adjustments, Lightroom clearly does not apply the adjustment continuously on the full-resolution image. Aperture does and, when you're used to seeing it in full-res, the Lightroom experience is less than pleasant: you have to adjust the slider roughly, drop the mouse, inspect the result, adjust more finely, repeat.
However, speed of using an application is about more than just how quickly an image pops up to the screen. I admit I'm still a novice in Lightroom, but I often found that I got confused about which of the five major modes I was in. The distinction between the Library and Develop modules seems an unnecessary speedbump in the UI, and it's not a distinction that is strongly felt in Aperture. In Aperture, you show the adjustments panel and/or the Viewer and you're in "develop" mode. Hide them and you're in "Library" mode. I made a lot of mode errors in Lightroom and the problem was made worse by the 'quick develop' panel in Library, which makes that view look a lot like Develop.
Very much like my earlier article A Subversion User Looks At Git, my conclusion is this: I have a much greater appreciation for Lightroom than I did when I started this review. It has some features that are better than my current tool, but it's also missing things that I critically depend on.
If Lightroom could lose the gothic makeup, get an export workflow and minmise the distinction between Library and Develop, I'd certainly be looking harder at switching. All that said, if Aperture just got faster (and supported lens model metadata!), I'd be equally happy.
Look forward to your comments.