Wich wide angel zoom is the best value for money?

Hello,

I am very tempted to start´photographing with wide angle zoom. I love the angles and the opportunity one has to be creative but I am hesitating about what lens to use. I very much enjoy working with small aperatures and landscape/ cityviews but I also want to have the option to take casual streetshots  and pics of happenings with large aperatur. Wich one is your favourite choise?

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kriztian