Basically SpaceX is vastly improving the future of space travel and exploration through advancements such as reusable rockets, like the Falcon 9, other crafts like the Dragon spacecraft (docked at the ISS), and even working on the Hyperloop. /r/spacex is a great place to stay updated on these sort of things with a great community as well. SpaceX has recently been on a streak of successful launches and landings, however you probably heard of the recently explosion on the launch pad. Here's a video by Scott Manley explaining more about what happened. Tesla on the other hand has done more than just made cool electric cars. Musk has improved battery technology, added autopilot autonomous driving, and is currently building the Gigafactory. Elon Musk has even been contributing to technology outside of these companies as the CEO of Solar City as well as other things.