I was looking for a sustainable electricity provider sustainability-wise (there's like a ranking from some Dutch consumer group I don't remember about). What made me chose this one over others is the ability to "buy" a part of a solar farm somewhere in the Netherlands. I thought it was a gimmick but it does offset a good part of my consumption.
Then they added the possibility to have dynamic pricing (I was an early adopter!), so I set my water heater to run during peak solar hours, and try to do my laundry on sunny days, when electricity prices are generally lower.
As a customer you get an app/website which is quite basic but that's a good thing: it's fast and you have the data you need and nothing more. Downside: I wish it was also in English, and there would be some kind of API to be able to do some home automation (e.g. get a notification when it's the best time to do laundry regarding my schedule and dynamic prices... but I can already do that with the ENTSO-E API + data you find in the contract).
Customer service is also really nice and friendly. I only had to interact with them when becoming a customer (they didn't believe that my building energy consumption estimate was so low, heat pump FTW!), becasue I was an early adopter of the dynamic pricing and because I found a bug in the website (which they quickly fixed!). For the first two things they insisted over email that I call them back (I'm really not a call person, my phone is permanently in silent mode) which I found a bit annoying, but that's really the only thing.