The people I consulted with suggest to develop for both and to release at the same time unless iOS and Android.
For cross-platform development I was told about Anywhere Software and their Basic4android / Basic4iOS. This is because people who are comfortable with classic Visual Basic can jump right into making modern apps once they learn the API.
The big concern I have here is the cost associated with this. What would you recommend doing if we have limited resources and capital to execute and launch a first early version of a mobile app?
There is solutions (e.g multi-os-engine.org) which allows starting by creating a standard Android application, and then rewrite only the User Interface components to deploy on IOS - assuming the components architecture is well split in different layers (e.g. MVC) . This offers the advantage of a shared code base and native experience, while not spending critical resources too early on the two platforms which requires different developer skill-sets usually.
iOS will be the fastest to develop for as it has a better developer experience and better community support. Since there is also less fragmentation among users, there are less edge cases you need to deal with. Most companies go iOS first for good reasons.
For cross platform solutions I recommend React Native.
From my mobile experience, general rule of a thumb is to go with the platform you know you will have the most users from (and/or revenue).
It's way cheaper to build only one app first, and test it against the market, and proceed with the second platform (for example: start with iOS then Android).
An exception is if you have really innovative idea (for example of a game), that you know could be easily ported to second platform (read the case of 2048 game), in this case I'd wait with the release until both apps are ready. But honestly that's an edge case.
If I were to build my next web app, it would be surely with react-native. It gives excellent ui responsiveness with shared logic across android and ios making porting effort seamless and time to market short for the second platform.
The first thing to consider is your customers, not the development tools. You don't mention what kind/category of app you are looking to build, who the target market is, is it a worldwide audience or is it US or regional. Is it feature rich and technically challenging, or is it a couple of screens or content? These factors will help point you towards IOS-first, Android-first, or platform-native vs. cross platform.
There is no one-size-fits-all universal answer. Some kinds of apps lend themselves to being "mobile web" and can be built using react, ionic, etc. Others you will find that customers simply demand a level of responsiveness, navigation and interactivity that can best be delivered by a native app.
Once you've understood customer expectations based on the kind of app, its feature set, and target geographical regions, you can better assess the pros and cons of leading with one platform vs. another, and native vs. mobile web, and you can then think through the different tools that claim to make it "easy" (not always true and there are always downsides).
If you do decide native is the way to go and your target market is US, its fairly common to see companies lead with an IOS version first, with an Android version "soon". Aside from everything else, it gives you a chance to get customer feedback and response on your product before you make a major investment in developing two versions, or make a serious commitment to one of the cross-platform toolsets.
Visual Basic has been obsolete in various senses for at least 10 years. That would be a terrible choice. You don't want to work with anyone who is 'comfortable with classic Visual Basic'. Nobody should be comfortable with that anymore as practically every other alternative is better.
There are some reasons to do native development for each platform (Java+C++ etc. for Android and Swift for iOS), but it is probably a good strategy to try a good cross-platform solution first. This is especially true for less technically demanding apps.
One nice thing about Flutter is that you can build part of your app in Flutter, part in embedded web views (maybe even with Cordova), and anything else you need natively.
To be honest you have to wait and survey the market first by comparing Android users to iOS users and that will tell you which one to release first
Look at a cross-platform solution like React Native. And in the rare case that you need too much custom functionality for that to be a worthwhile approach (lots of hardware specific implementations, for example), unless you have a really urgent launch date, there's literally no reason to develop both at the same time unless you have every possible interaction and screen worked out and professionally designed already.
Develop in one, user-test/work out the bugs, and even release, and then develop the other. Anyone telling you they *have* to be done in tandem better have a good reason.
I do agree with the experts here. You should do market research first and conclude the approx number of audiences using android or iOS devices. That is one option.
Another way you should go with is developing a hybrid mobile app. With a little customization, you can run your app on each mobile platform.