I hope it's ok for me to say this (I know this is my first post, just bought US2 2 days ago): Try Space Engine if you like pretty Space pictures! Do you know this game/program? It's free in it's current state. Universe Sandbox is great, but not really focused on looks, it cares more about physics.
Agreed, though it is MUCH easier to create custom systems in US2. What program you should use really depends on what you want to do, how many customization options you want, and how long you're willing to wait to get the "results" aka an end product. US2 is a great way to make star systems and check if they're at least plausible, as it's very strong on physics, but it lacks in the visual aspect compared to what you can get elsewhere. For making planets, the options I know of and use are Grand Designer and Terragen. If you want pretty good planets with wait times of at very most a few minutes unless there's a bug, Grand Designer is the way to go, but if you're looking to have more detailed and greater customization options as well as highly realistic visuals at the price of possibly having to wait hours if not days (for very complex scenes) for renders to finish and the money needed to buy the program, Terragen is better. If you're looking for visuals and don't care about customization, Space Engine is great. It just really depends on what you want to do or see and how long you're willing to wait for it. Though, don't take this post as saying US2 can't do much, it can do a lot of great things (As far as I'm aware its the best and easiest way to make star systems and tweak them to your liking without having the headache of editing one or more files and in some cases doing lots of converting file types) its just that other programs do things better depending on exactly what you want to do and honestly its probably easiest to use lots of different programs together to create what you like. And for the times you're bored of creating and just want to explore or want to put the extra effort in of doing what's needed to create, Space Engine is there.
Apologies for the wall of text, I could tell about my creative process with these and other programs but I'd rather not have anyone fall asleep and break either their keyboard or their face :-I