Inkscape: Completely capable. I know many people who have used it instead of illustrator professionally for years.

GIMP: Depends on you. As someone who learned GIMP long before ever learning Photoshop, I find Photoshop unintuitive and frankly stupid. So it's all about what you learned on. But GIMP relies on spending a few minutes setting it up for your own use case. Literally every window can be moved to anywhere. You can have whatever windows you want open all the time, or hidden behind right clicks, etc... Your tabs and tab groups are completely customizable to how you want to work. BUT the rub is that you have to be interested in doing that. GIMP is trashed for having a bad default UI because the expectation is that it doesn't have a default UI. My GIMP would look entirely different from someone elses because I use different tools that I want front and centre than someone else might. If you're not interested in that and just want something that you can learn a "default" setup and go with it (and there is absolutely nothing wrong with that) than you're better off sticking with Photoshop.

As for Krita, whatever else people are telling you, Krita is NOT a replacement for GIMP if you're doing design work. What it brings to the table in terms of having built in Vector capabilities it negates by having a very limited and basic suite of selection tools. Something that would take you two seconds in PS or Gimp to band select, paint the foreground, feather the selection, shrink it, etc... takes five extra steps in Krita because Krita is a drawing program not a graphic design program; what few "advanced" selection tools they've introduced is tacked on and hidden between three or four extra steps because it just wasn't designed to have them at first and they were added later.

Just because it looks nicer out of the box than Gimp, doesn't make it better. I've tried replacing Gimp with Krita because i like the KDE suite of apps in general. But I was pulling my hair out trying to do even a basic composition using it's archaic selection tools.

I actually really enjoy GIMP as an alternative to Photoshop. My biggest problem with it is that Photoshop keybinds are muscle memory, and for whatever reason GIMP has everything totally different so I almost always end up having to hunt down what I'm after.

I've heard there are ways to get it 1:1 but I've never been able to figure that out. Admittedly, I haven't looked too hard either.

In my experience, Inkscape can be used as a professional replacement for Illustrator. It has never crashed on me. There may be some limitations, but nothing super inconvenient or something there isn't a workaround for.

GIMP, on the other hand, is a mixed bag. I believe Krita is a much better candidate to be used professionally than GIMP. GIMP has an objectively bad UI, has weird quirks for very simple tasks, and is prone to crashes. I use GIMP for simple image editing and Krita for more complex projects. GIMP 3.0 is their best chance to fix their reputation and I'm hopeful it will deliver.

If you don't have time to try them yourself, follow creators who use them and check their workflow. I recommend Davies Media Design on YouTube for great videos on Inkscape especially.

Edit: No program is completely immune to crashes, it's good practice to routinely save projects no matter how stable or unstable the program is.

I'm surprised to hear GIMP crashed on you, I don't think I've ever had it crash on me.

Its very easy to use and my goto image editor, but I say that from a position of familiarity of having learned where everything is and what all the keybindings are over many years.

In contrast, Krita seems like a far better image editor, but because the interface is bewildering to me, I've shied away from it.

I've been using gimp's 3.x branch since 2016 or so (after getting a hidpi display) and gimp itself since the early 2000s, both for personal stuff and for work. I'm typically editing existing photos and images to clean them up, apply effects, make new clean images from pieces of existing ones, etc, and for my uses it's great. Also, having been using it for so long, I actually really prefer the ux to Photoshop (especially since they added an option to use it in single window mode).

I've seen videos showing some of the features it's missing for certain types of things though, and while there are hacky scripted ways to emulate them, you might find it lacking if you're expecting those particular features.

I'd recommend looking up tutorials on YouTube for things you frequently do and see how much work it is and what the final product looks like. You could up the playback speed to save time since you won't be following along with gimp yourself.

Honestly it's better but still a mess of design choices. For open source graphics editor check out Krita.