I do not agree with the opinions here, that LR seems to be the "default" way to go after Aperture.
I spent a month comparing LR and C1 Pro (from Phase One) side by side, to give me a thorough overview of the strengths and weaknesses of both tools. I knew both LR and C1 already, LR from testing out previous versions here and there (never liked it) and C1 for being my default tool back in 2004 when it was in version 3.6 just before Apple released Aperture.
What I always liked about Aperture was its great interface, the very well designed database approach, which allowed for excellent scaleability, the overall ease of use in the quest to "replace the finder" and the great customisation options of the whole interface and workflow. I was a Aperture evangelist basically from day one. So that's what I was looking for in LR and C1 mainly.
After my tests, LR was just as bad to work with as it was with its first version back in 2007. You can not customise sh** for your workflow. You can not even adjust the keyboard shortcuts. You can not put the adjustment panels on the left side if you are left handed. It has never tried to replace the finder with a slick database, you are always forced to look after your files on the finder level on your own. It was always designed for one screen and one screen only, even if it later added multiscreen support. And its image quality, while it was maybe slightly better than Aperture, did not really blew me away.
C1 on the other hand has major shortcomings on the DAM side and is a much less solid database to work with. The interface is a bit weird, but at least it makes good use of screen real estate compared to LR. Image quality is top notch, it is absolutely stunning and second to none. Color editing and grading is pure joy. And what was one the major strong points for me: it has an even MORE customisable interface than Aperture. It actually allows you to create a floating window for every single adjustment panel there is (and there are a lot), put it anywhere you want it and then save the whole setup as a workspace. Adjusting the keyboard shortcuts allowed me to bring back my "muscle memory" from Aperture. And it has the same referenced or managed approach to handling your assets. You can throw all your images into the catalog and have it handle all the files in the background for you. So to my surprise, it was MUCH closer to Aperture after testing it than LR ever was, despite everybody talking about LR as the "obvious" migration path. Just not true.