Im not sure the two can really be properly compared. They both play completely differently. There are some obvious things though that can be compared but keep in mind the two games are as far as they can be apart and still be in the same genera.
Space movement. ED is more like a plane in space and SC is more 6dof space combat that normally ends in space jousting. I like SC combat better but there was nothing wrong with the combat in ED. I like both but SC felt more like space combat.
Content. ED has tons more content. Even after it is 100% released ED will have more content in that the number of systems are so vast. SC has only confirmed 100 ish systems and currently they only have 1 system with 1 gas giant, 3 planets and 12 moons. But what they have per body is a lot more detailed and interesting than what ED has
Missions. ED has many more missions but SC missions are more in depth with more things to do. Most of ED missions are kill X, deliver Y etc. In SC you still have those types of missions but you also have to search abandoned space stations in EVA or infiltrate a luxury liner that has been hijacked or go down into a cave on a moon and search for someone who has disappeared. It's hard to say that SC missions are better because they are a lot buggier but they feel more varied and interesting.
Economy. ED has a huge and functioning economy. SC has a very small and barely functioning economy. On top of that every major patch they reset your profile and you have to start from scratch again. (like how ED did it when it was in beta). But every patch SC getting a little better and the economy expands. They have also stated they want to move away from the per patch reset and move to only resetting when it is absolutely needed. But they are not there yet.
Ships. ED has a lot of ships... SC has more ships and they are of higher detail. Here is a comparison picture. (not all of these SC ships are in game but a lot of them are) ((large) https://i.imgur.com/yeY48SH.jpg
) ((Medium) https://i.imgur.com/vZPtWZ8.jpg
) Keep in mind that all of the ships larger than a fighter have functional interiors you can walk around in and move cargo around in and drive vehicles into... It's hard to explain how significantly different and better that is over ED until you've tried it out yourself.
The biggest thing for me is that ED felt like you are the ship and not the pilot. The ship personifies you in game and when it dies you respawn back at a station. In starcitizen you are the pilot. You can move around in the ship, you can move around outside the ship and you can go about your business after someone has blown your ship up.
I dont think SC is better than ED, its a completely different game but I prefer it to ED even with SC being so buggy. But it depends what you are looking for.
But I wouldnt encourage you to buy the game blindly... they have "free flight" events every month or so where anyone can try the game for free. You just have to make a free account and download.