Will the wallets created at this moment in time be backwards compatible in the future? (Metropolis, Serenity, ...)
I can confirm that MyEtherWallet will always provide backwards capabilities with older version of our encrypted versions, as well as common methods created by other wallets. We are currently in the process of switching to use the same encryption as geth which will (1) help standardize across wallets and (2) make it easier for people to move from MyEtherWallet -> Mist in the future. We also hope to implement other methods of accessing (ie: Jaxx mnemonics, etc.).
For reference, the only things that might change as Ethereum "grows up" is the json / keystore / encryption / etc. formats of the private key. In the end, it's still decrypting to get to the same version of the private key. The way you store it and decrypt it just might change. Most, if not all, wallet providers are going to stay up to date as encryption methods and standards emerge and provide backwards capabilities and cross-capabilities.
How do I verify if the wallets have been created correctly (private key), without first sending a small amount in and out of the wallet?
Personally, I use the MyEtherWallet offline transaction tab to test in and out of any new deep-cold-storage wallet. I suppose you could import the key using a different client and verify it gives you the same address. So, since you are using MyEtherWallet which using Javascript, you could import the unencrypted private key into geth and verify the address, or into eth, or whatever. You will not want to cross-verify with another Javascript implementation (like EthAddress).
Is there anything else I have to consider and I am correct with my assumptions?
I recommend keeping a copy of EthAddress or MyEtherWallet's zipped repo with your cold-storage keys. That way in the future if something changes or something, you'll still have a local version, one that you know works with your private key, to run.
Why are there only third-party web wallet creation pages on the internet and no official ones (yet)? (Maybe because of: Ethereum: "We are making tools for tool-makers“?)
The Ethereum developers have stated that they are working towards a light client. At this point, I find it impressive that they have so many clients in different languages and the Mist / Ethereum Wallet is already as strong as it is. It's been 7 months since launch. Also, keep in mind that the Ethereum Wallet / Mist is so much more than a wallet. A lot of people seem to forget this because that's all they use it for. But in reality, the things they are doing with contracts and tokens are amazing and is what they are focused on at this point.
For reference, here are the three sites mentioned in this thread:
full disclosure: I am co-founder of MyEtherWallet. I try to be objective.
Based on your description of the story so far, you're mining in the simplest way possible (Just confirm it's testnet and mining enabled).
Patience is the answer. TestNet is usually not competitive, but you might need leave the computer alone for a little while to see results. In the past, I've achieved good results letting it mine while I sleep.
Hope it helps.
Best Answer
There is no "official" when it comes to crypto. It definitely depends on your desire for security, how much you are going to be holding, what you plan on doing with the ETH or tokens stored there, and more.
I recommend that people use whatever tool they can understand best and use with confidence. I do NOT believe that recommending someone who has never used command line to use geth. There's too much room for error and it deters people from investing and getting involved.
Regardless of what tool you use to create an account/wallet, you should always safely store all of the necessary information in multiple places. Multiple places means multiple physical locations. If your house burns down, that computer and piece of paper are both gone. Read the instructions. Ask questions.
Here is a list of trusted wallets I've put together.
Last Updated: April 2019
CLI
Geth (go implementation): Command Line, Official
Parity: Rust implementation
Hardware Wallets
Ledger - Can be used with MyCrypto, the Ledger Live Desktop Application, iOS app, Android app
Trezor - Can be used with MyCrypto or Trezor's web app
Keepkey
Desktop Applications
MyCrypto — also has a web version with support via Ledger, Trezor, Safe-T Mini, MetaMask, Parity Signer.
Exodus: Desktop, multi-asset wallet with ShapeShift integration
Mobile
imToken - iOS, Android. Longest running mobile solution for Ethereum. Dominates in Asia, tons of features, for some reason just hasn't quite breached the western market completely.
Trust Wallet - iOS + Android, dApp browser
WallETH - Android, Open Source
Parity Signer - Turns your old phone into a hardware wallet / transaction signer. Super safe. Can use with MyCrypto
Ambo - iOS
No Longer Maintained
Mist Ethereum Wallet: GUI, Official, Full Node, App, Supports ETH, Generic Token Interface, Generic Contract Interface
Eth (c++ implementation): Command Line, Official
Icebox: by christianlundkvist @ ConsenSys, Primarily for Cold Storage, Downloaded, Open-Source
EthAddress.org: by ryepdx, GUI, Client-Side, Website, Can be Downloaded, Open-Source
ethereumwallet.com: By Kryptokit, GUI, Website, no longer under development (see Jaxx)
EtherLi: Multi-sig Ethereum Web Wallet, GUI, Website, online