Mobile operator and plan choise for startup (Duesseldorf)

Hello All,

I'll be staying here in Düsseldorf for a couple of years for work. And was wondering what would be the best mobile carrier and plan ( cridet or prepaid ) to use for a local number.
Currently I'm staying at a temporary address untill I find a permanent one in 2 months. And I use mobile internet quite a lot at least for search and map directions.
But I also want to control my spending or at least monitor it closely for the first couple of months.
My German is also bad and would need good English customer support service if any is needed.
Let me know your thoughts, sorry if the topic is a duplicate, kindly point me to any previous discussions about the subject.