Hello Trinita,
I wish you a safe arrival in Offenbach.
If you have an apartment in the Goethe Quarter, you will have a fiber optic connection.
As far as I know the providers are all similarly reliable. I myself was with Vodafone in the meantime and now again with Telekom.
I recommend you to check24 (you have to check your correct address) for the desired flatrates (Internet, fixed network TV) plan router inclusive?, because not every provider has "everything" you might want in the offer.
Many greetings