Birdwatchers use 8x42 if they have a scope. 10x42 is preferred as the only binoculars, especially if you will likely watch from large distance in open country - like with eagles.
In practice, quality of binoculars is as important as the nominal magnification. Here first choose the budget you are comfortable with. Then it is best to check models by yourself, in a shop or on special field optics days. Ask to take the bins out of the shop and try watching e.g. chimneys, or pigeons on a car park. Otherwise there is plenty of online advice about good bins within different price ranges.