I have been using Bitcoin for over 10 years and have never used the testnet. Testnet is a tool for developers. Therefore, I recommend all beginners to use the main network right away. You can buy Bitcoin for 20-30 dollars and try transactions on several wallets.
It's true it's initially created for developer, but i don't see anything wrong used for learning/testing purpose by non-developers
assuming they follow well-written guide or have someone guide them directly. Besides, I've seen other thread where they claim they use testnet to teach people how to use Bitcoin.
The fastest and most convenient wallet in my opinion is Electrum.
I agree. But FYI, Electrum on Android doesn't offer testnet option unless you're experiecned enough to build testnet APK version from source code[1].
[1]
https://github.com/spesmilo/electrum/issues/5570