Hi Mikael, I would say that in Stimulsoft JS you can design and get report web preview. You will depend on the browser memory for showing  the report, and if you have a large report , you need to remember that the whole logic to create a report is client side, so it can be a little problem.

Ex toolbar (JS):

On the other hand if you use the .NET Stimulsoft the report is generate from server, all logic is there. This way you can create larges reports but you only can manipulate binary file. you can download that, send by email or whatever can do with a binary.