The general rule of thumb is that appliances should be installed before countertops. This is because appliances need to be properly secured to the underlying cabinets, and it can be difficult to do this after the countertop has been installed. Additionally, appliances must be properly aligned with the countertop, and this is easier to do before the countertop is in place. However, there are some exceptions to this rule. For example, if you are installing a cooktop or range hood, you may need to install the countertop first so that you can properly measure and cut the holes for venting. You should always consult with a professional kitchen designer or contractor before making any final decisions about appliance and countertop installation.