What is the best photo editing software to replace aperture

Question

Because Apple has decided to no longer develop Aperture, what are the best valued, most capable programs to replace Aperture?

Answer 1

Regarding the "ship shape" comment: you might want to look at some other products just to see how they would handle importing images. There is a lot of chatter on that subject for obvious reasons. What you don't want is all your info being stuck in a format that is difficult to retrieve.
First, consider referenced photos instead of the library. The managed library of Aperture/iPhoto is pretty unique to Apple. Sure, things like Lightroom's Aperture importer will copy those photos out for you, but it's a work around. If you have a photo structure in the Finder, it's always available no matter what you use, DAM or browser or just Spotlight.
Second, consider preserving your photo adjustments. Think of them as printed pictures. The adjustments (except really simple stuff like maybe crops, etc) do not carry over to other image managing  programs per se; the way to preserve those adjustments is to export the photo as adjusted, say in a TIFF. That's what you may have noticed that plugins like Nik do: they don't pass adjustment INFO to Aperture, they pass an exported photo. Consider a workflow that does the same. Even if the new Apple products or whatever comes next is what you wanna use, it may be useful to have these. Some of the cool adjustments demo'd in Photos might translate exactly from your Aperture info, but maybe not. You might have to start anew, and having at least an exemplar might be nice.
Third, make your photos application independent by writing in metadata. The cool thing about image files is that even your garage door opener can probably open them. They are really universal. AND so is the exif/IPTC/XMP metadata within those files or sidecars. So write it in there. You can replicate a whole Project/folder/album or collection set/collection just using heirarchical keywords. And another cool thing is that this info is available in the Finder, in other operating systems, and with searches via Spotlight. It's tremendously powerful and many Aperture and Lightroom users, who often are solo users, don't make enough use of it. Those who worked with other people/departments etc probably use this more often; Photo Mechanic is the epitome of this. Metadata in photos is far more powerful than even tags in the operating system; it's like a DAM grafted into your files.