I have been researching this for a while. I own Lightroom already as part my company's CC licensing so have been trying it out. I also downloaded the trial versions of Capture One and Media Pro and have tried them. I have also been dabbling with Photos - I use it at work.
I'm not a professional photographer - my use of Aperture is to organize our family photo archives. Professional photographers have different needs than someone like me. Pro's need to manage smaller projects...and many of them. A family archive can be one huge library, as it is nice to have access to all photos. Also, many family photos are going to be taken on iPhones due to the convenience and ability to capture spontaneous moments. So iPhone friendliness is very important. This isn't a priority for Professional Photographers.
I think Lightroom is the closest to Aperture in terms of features. It has a nice import from Aperture, which can bring over keywords and albums. But as Leonie said, the interface is not exactly inspiring. And for whatever reason, their processing of previews makes the interface extremely sluggish as opposed to Aperture which is lightning fast. The other thing is that, for some reason, it added some extra characters to the file name of a bunch of my iPhone photos, so when I import from my iPhone it wants to re-import like 600 duplicates. This is a big problem for our family libraries.
Phase One's Capture One is absolutely beautiful. And together with Media Pro, it goes way beyond Aperture. It also has a nice Aperture Import feature. However, it is a two step process - you ingest into Capture One, then transfer to Media Pro for the library features. You CAN use the Capture One library without Media Pro, but it's library features are weaker than Aperture's. For some reason Capture One won't even recognize my iPhone for import. The Phase One solution caters to professional studios. The two step process and the iPhone issue are problems for me.
This brings me to Apple Photos. The conversion from Aperture is good. (You do lose the 5 star ratings and some other features though)
- It automatically organizes by Years / Collections / Moments, which is close to what I did in Aperture (manually) which is Years / Months / Days. This will save me time.
- It is the most iPhone friendly solution (which you'd expect). Don't have to worry about importing duplicates. Your edits on iPhone will carry over to Photos.
- It is Integrated into other Apple software - for example: Apple Mail and iMessage allow direct export straight into Photos.
- iCloud integration - Cloud storage is the future. You will be able to edit your photos on any device. You will be able to share online albums with other family members. Your photos are automatically backed up.
- The editing tools in Photos are powerful with the 3rd party Extensions and now the ability to round-trip edit with the external editor of your choice.
- Apple Photos is geared toward Family Photo Archives (perfect for me). It is not geared toward Professional Photographers.
- Photos is young, so I'm looking forward to big improvements in the future.
My choice is Apple Photos. However if you are a professional Photographer you should take a look at Capture One+Media Pro or Lightroom.