Upload & Sell: Off
I used Aperture from 2006 when it first came out till January of last year. I now use Lightroom although I continue to maintain my Mac/Aperture environment and do use it occasionally.
I had built a Mac Pro specifically for running Aperture. For a long long time Aperture was REALLY slow compared to lightroom and had lots of painful things. Apple has always been more forward looking than Adobe when it comes to offloading processing to the GPU but this was a 2-edged sword most of the time as there was always going to be a combination of adjustments you could put on your image which would completely destroy performance. (Seemed to vary based on camera, ISO speed, and combination of adjustments)
I also had major problems with Aperture creating hard drive fragmentation. Apple claims their filesystem doesn't fragment but they are basically lying. Their definition of "doesn't fragment" is a typical home non-serious user using the machine for a year or two before upgrading to a mac. Under that scenario those users will never see degradation of performance from fragmentation.. but heavy Aperture use will really fragment the drive due to the way it stores the library. (As a software engineer, Apple's library design of XML files is terrible compared to Adobe's use of an embedded SQL database.)
They both have their plusses and minuses... for me I have found Lightrooms keywording to be much better. So much better I actually keyworded like 60,000 images in it relatively painlessly when I switched, and I now keyword everything on import. I could never get myself to be good at this with Aperture. But Aperture's import & preview generation is considerably faster. (I have lightroom generate 1:1 previews just like Aperture does, so once they are done it is fast, but it does seem slow to do it.)
For my purposes I prefer ACR over Apple's raw conversion. Apple's is not bad at all, and does some things very nicely, but Adobe's does a much nicer job of eliminating noise while retaining detail, and Apple doesn't have Camera calibration profiles.
In terms of community, Aperture doesn't really have much of one. There is far less documentation, training, books, presets, plugins, etc.. available for Aperture, partly because who wants to build anything on top of an Apple product when Apple gives no clue whether the product has any future? Adobe may be obnoxious with forcing people to use the cloud but I would find it very hard to believe Lightroom is in danger of being cancelled or won't have continuing development.
Aperture also has some color management issues.. they don't have printing quite right, and there have been a lot of bugs on the way to it getting soft proofing working. When I stopped using it last year I believe there was no way to specify the rendering intent in a print preview, even though you could pick the rendering intent when soft proofing. There were also bugs in the saving/loading of presets that would ruin prints when they hit you. Things like that were pretty annoying. With Aperture I ended up printing from Photoshop for anything critical, with Lightroom I have been able to avoid using Photoshop for print, and I have built up a great set of presets that save tons of time.
I ordered quite a few hard cover books through Apple's service, they do a good job with that. I haven't had the opportunity to do that through Lightroom.
Integration with websites, services, etc.. works much better in Lightroom in my opinion. I have used the Smugmug and facebook uploaders in both products and have had much better luck in Lightroom. That can save a lot of time.
Personally I also feel like there is a big risk with Aperture in terms of completely tying yourself to Apple as well, they are very prone to dropping support for hardware that is still very powerful, etc.. if you are locked into the Mac you may lock yourself into a relatively fast upgrade path on expensive hardware. My PC lightroom setup is about 1/3 the cost of my Apple/Aperture setup, and if I was to try and setup a new Apple/Aperture environment today the cost differential would be even larger. My Mac pro is 4-core, 2.66ghz, $400 video card, 4TB of disk space, 16GB ram, etc.., and yet apple dropped support for the machine entirely in Mountain Lion. Not exactly a good way to get me to drop $3000-5000 on a new Mac Pro to continue to stay on a supported path.