You should prefer orthoimages from national or federal mapping agencies. They will often diverge from each other, as they have different resolutions and quality standards. The process of correcting aerial images for topography is called or tho rectification, and a digital elevation model (DEM) is required for that. It has several downsides, one is that there is more distortion in high object like buildings. A quality standard in Germany for example is the TrueDOP (DOP = Digital Orthophoto). You can read more about it in this article if you are interested.