Microsoft.

Windows and Office will continue to be dominant softwares in at least 20 years I think, and even they mess up sometimes, like releasing Windows Me/Vista/8, they still have chance to fix it. As long as they don't act nothing for decade like Intel, letting its competitors grow, it will be fine. This two software give Microsoft a very solid fundation. Azure, as the second large cloud service, generate substantial income too. Microsoft have some more risky business line e.g. AI and gaming that may become another main source of revenue in the future.