what is the best app to replace aperture?

A good question to ask of the support people at CaptureOne.

The issue here is that all parametric editors have their own versions of the various values they offer you. +3 on a red slider in Aperture is not necessarily the same as a +3 on a red slider in Lightroom or CaptureOne or anything else. So, each software will try to guess the values of the other one, and sometimes the results will be, well, interesting.

That said, the same issues arise no matter what parametric app you migrate from. It's just a feature of these apps.

Apple's solution is to generate full size previews before migrating. That way you get the original and a high quality version, at the cost of duplication and higher disk space usage.

The only way you will know this is to try it out and see. That's why these makers offer free trials. So, download CaptureOne and give it a whirl, see how it goes. If you're happy, all good. If you're not, try others, like OnOnePhotoRaw which also attempts to 'translate' the values between Aperture and its own system.

I am concerned about losing the thousands of adjustments I have made to images in Aperture. I'm leaning toward Capture One because I don't want to be stuck with Adobe's subscription for life. Does Capture One or any others retain Aperture's adjustments?

Thank you, TD. I have tested a bit and it is promising. But the Library size will be a problem. My main library is larger than the free version allows, so I have to move selected albums, not the full library. But the Photo Library Import does not seem to allow selected folders, only the full library. I would have to export the folders and reimport. I could not yet find a view, where I can see the titles below the thumbnails.

There isn't a "best" one because it depends on exactly what your requirements are.

Photos is not as good as Aperture as a DAM. but it can be its equal as an editor, using extensions that allow you to link to other apps. It's free. But it is, frankly, a consumer product. If you're a pro or serious hobbyist, if you're shooting Raw with a DSLR then I would suggest you look elsewhere.

Most people ended up with Lightroom Classic (as it's now called). It's a very good app, very powerful DAM and very good editing tools. It links effortlessly with Photoshop, unsurprisingly. It's also an excellent host for plug-ins like the Nik package, or can use some stand-alone apps, like Luminar or Exposure X5 as plug-ins. It can pass Raws to other raw developers like DxO PhotoLab. It really is a very good hub for your workflow. Downside? Some folks don't like the subscription model and that's now the only way you can get it. But it is very good value given that you also get Photoshop in the same subscription.

CaptureOne is probably the second most popular destination. An excellent raw developer, some folks are unhappy with its DAM. There's a bit more of a learning curve too (or that might just be me ;) ), and it is expensive. But it can be bought outright, or subscribed as you prefer.

Mylio is an excellent app that, capability wise is more powerful than iPhoto but not quite up to Aperture. But it is an excellent DAM, and if your goal is sharing across devices they're ahead of almost everybody.

PhotoSupreme is just a DAM, and quite a good one. But you'll need something else to process the photos.

Luminar is a well-marketed editor. I'm more impressed with the marketing than the editor. Exposure X5 has a rapidly developing DAM and is almost as capable as LR in many respects. It's well worth checking out.

OnOnePhoto Raw pitches itself somewhere between LR and Photoshop. It has elements of both. Bit of a chequered past, but the current version is positively received, like they may have reach a level that makes them a real player in the field.

DxO Photolab is a very good raw developer, probably the best for noise reduction and arguably, on a par with CaptureOne. It doesn't really have a DAM, or at most a very rudimentary one.

There's a few worth looking at. One thing about photography apps is there there are a multitude of review sites and photography blogs that will tell you a lot more about these apps. Youtube is especially worth looking at as there are thousands of posts there with folks reviewing, doing hot-to and the like.

Definitely, you need to get the migration from Aperture to a successor done, while you still can run Aperture, see: How to prepare the Photo Libraries before upgrading to Catalina - Apple Community

You need to be able to run Aperture to get your library ready for the migration. But it is hard to recommend a specific app. It really depends on your needs. You will have to pick an application, that will support a workflow you like. Download the trial versions and test them, before you decide on your favorite. If you need a professional application, you may want to try Capture One or Light Room, but there are many more to pick from. There are several good recommendations by Terence Devlin in this forum.

Re: Adobe's Lightroom Classic application. I have here and on other threads mentioned that when you cease to subscribe to the app it continues to work as a DAM just without editing. This has certainly been the case until recently.

However, discussion across the forums of various photography sites suggest that this may well be no longer the case. Various users report being told by Adobe representatives that once the subscription lapses then you will no longer be able to launch Lightroom Classic at all. Several users report finding this out the hard way.

The webpage that tells us that you can continue to use a limited version of Lightroom Classic is still up, but it is now at odds with recent reports.

I offer this simply as information. Make if it what you will.

Thank you for this warning, TD! 😒

I just have been thinking about giving Lightroom another try, after encountering so many issues with Photos 5.0 on Catalina. And all my Skylum.app are no longer supported on Catalina, only Luminar 3 has received an update.

Have you checked out Mylio? It's quite deceptively powerful. As an editor it's adequate but it can send a file to just about any other app you choose and, if you save from that app into the original folder, the new version pops up in Mylio a couple of seconds later. The DAM is good, the calendar, places and faces views are very good. It looks a bit like a consumer app but it's pro-level powerful. It can sync across multiple devices and not use the Internet, just your own wi-fi. Been trialling it here for the past few weeks and thinking seriously about moving over.

What is really tempting in Mylio, is to see rating stars again and color flags. And slideshows, that can automatically show the titles. But it is also a subscription model, at least for the size of my library.

I'll have to test, if Mylio will allow me to work with Live Photos, Portrait Mode Photos, Videos.

The missing support for Live Photos in slide shows is my biggest problem with Apple's Photos.app. I am taking more and more Live Photos with my iPhone, because I like to see the pictures of animals and waterfalls animated. But when I want to use them in a slideshow, I have to convert the Live Photo to a video.

Does Mylio show titles and ratings on the iOS devices?

On iOS there are three basic views: Thumbnail - this shows the star rating on the thumbnail

Medium view - this is the image plus Info Panel. This includes everything that's on the Mac OS information panel, including titles.

100% View is just the image scaled to the device size.

This is on my iPad. Haven't checked the phone yet. That said, this testing is all done on the free version. I believe the difference with the full version are: editing Raws in Mylio (not a feature I'd use anyway) and library size.

I have not yet tried it, but it sounds good. Thank you.