Electrum is Bitcoin-only, right?
If so, it does not fit my need since im looking for something for Ethereum/Ether.
As I said: For me, Armory is the perfect Bitcoin-Wallet, but I cant find a good solution for Ethereum.
There isn't a decent desktop SPV wallet for ethereum. I know this is weird, but this is true. (I don't know how ethereum is this far without a decent desktop SPV wallet)
For Ethereum, the best wallets are browser/mobile. For example, MetaMask and MyEtherWallet. You can also use multicurrency wallets such as Exodus (desktop) or Coinomi (mobile)
Metamask (browser) is probably the best implementation.
Additionally, if you have a hardware wallet you can use Ledger Live or Trezor Suite, which are good desktop multicurrency wallets. They allow you to check balance without the hardware wallet device, so they are also watch-only wallets.