Which is more valuable: technical or personal experience for career?

I am facing a dilemma where I can choose to go for a medium startup, with a relatively consolidate team (I lot of work to do of course) where I would work with Data Streaming, Functional Programming and Machine Learning, basically everything I've been studying for last year. There is also an option to go for a really small startup (4-5 people) where nothing is defined and I would be the guy to work in every aspect of the company, probably not technical challenge as the former.

Which path should I pursue in the beginning of my career? I love the small and starting a company aspect, but I feel that if I am not working with high technical challenges I will not be able to catch up later and miss opportunity. Any insights?