If you want a deterministic wallet that only needs to be backed up once: Armory or Electrum. For features, ease of use and convenient cold storage I think Armory wins over Electrum. Try both out, choose for yourself.
I have chosen Armory.
But is it also good for an "everyday transactions wallet" or is for this purpose electrum better?
Armory will administer many Clients
If you make "everyday transactions" with e.g. Electrum ,Armory will show the Balance of all Clients, right?
In total or the different Clients separately ?
Can I run electrum by USB-Stick?
If you have more than one wallet in Armory the balance of each is shown separately. Electrum has a portable version that runs from a USB drive. Install both and try out.