I was wondering the same thing. Our startup currently uses it when doing research on data sets, but it's a db I don't hear about very often when talking about startups. I'm assuming a big factor is price.
I would say all these databases are worthwhile as long as the DBA is competent. Given that, unless you have a reason to choose Oracle (e.g. familiarity, integration with other applications, a specific Oracle only feature, contractual obligation), I see no reason to choose Oracle. Many companies choose Oracle because Oracle built a solid database/brand early on while catering to big businesses. MySQL and Postgres made great progress in the past decade make them valid alternatives.