Which IDE is Best for Ionic 4 for App Development ?
Whatever you are most comfortable with.
VS Code works pretty well for Angular and TypeScript.
This thread might be interssting for you!
Same as this link.
https://ionicframework.com/docs/developer-resources/editors_and_ides/
I started with Visual Studio but found it didn’t handle Typescript well. So I moved to Sublime because that’s what @joshmorony was using, at least when I asked him at the time. But I found VS Code easier to use than Sublime, and I’ve been very happy with it. I’ve never tried WebStorm or Atom (both are supposed to be excellent) but I’m happy sticking to VS Code.
If I can add this:
VS-Code works on all platforms Linux/Windows and Mac. Its leightweight, doesnt need much resources as it doesn’t need much space on your harddrive. It has GIT implemented so you still can connect to your repositories. Works well with TS/HTML/Angular. I still prefer VS full power but if you are only working with Ionic I think you will be very happy with VS-Code.
I use Webstorm and I’ve to say I really like it, I would not change. It maybe consumes more memory than Sublime or other, I guess, I didn’t really compare, but it’s because it indexes everything in order to let you search instantly across your all project
Also it is really super powerful when it goes to refactoring, I honestly would have trouble working without this feature and without the fact that I trust it
I recently played with VS-Code a all day and I have also to say that I thought that Git is better integrated in Webstorm. Most importantly you could stash changes in different changes list more easily
When it comes to the price, so yes Webstorm is not free, but I’m fine with it because each time I’ve got a problem I don’t hesitate, I contact the support and I always receive an answer almost within an hour
oh I almost forgot, may sounds totally silly, but in Webstorm you don’t have to save when you are typing or editing something, it saves everything all the time and provide a local history (like a git history but a local one)…may sounds silly but the day I used VS Code a couple of times I was surprise to not find my modification in my test app when I finally figured out “fck I forgot to hit Ctrl+S” 
VS Code is one of the best IDE for IONIC.
I also go with Visual Studio Code, it gets the job done smoothly