Regarding electricity contract

Hello everyone

Which electricity contract company will be cheaper ? I am going to live alone with 1 big room, 1 kitchen and 1 toilet bathroom. Please let me know how much energy I should state in initial contract ? I am completely new to cold rent concept. So I don't have any about my electricity consumption. On Check24 site there are option like e.on, NaturWerk, Octopus, Vattenfall, Eprima. Also please suggest if you know other cheap proviser.