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@witze From a development team and leadership perspective definitely SIA. From what I see in terms of marketing, PR, ease-of-use Storj. Storj looks like Dropbox to me where as SIA like S3. Time will tell who releases a method to access files directly through the browser earlier, who gets its performance right and if it is an infrastructure play that wins because of developers or if "marketing" will win. There were services in the past that weren't technologically great but still got a huge market share because of their marketing.
In terms of user adoption being able to just buy storage with a credit card (Storj) and not need to get a specific coin (Sia) is definitely a huge plus...but maybe filecoin puts them all to shame :)

Pretty good answer and more or less my opinion, I m also prefering Siacoin, but Marketing doesn't look the best. What are your favourite coins btw. ?