Corporate Strategy & Dev after undergraduate

Hey all, 

I'm a senior graduating this summer. I received an offer from an economic consulting firm (think Analysis Group, NERA, Cornerstone, Compass Lexicon, Brattle). I've been interning at a growth stage startup (400+ employees) this semester for their Corp Strategy & Development team. The position was for originally MBA students, but I managed to work my way in by networking and leveraging my previous internship experiences in IB. The start up recently gave me an offer to stay with them after graduation and I'm very conflicted. 

Going through the typical analyst program at an econ consulting firm will help me get into a decent MBA program and open doors for me. I am interested in the finance problems that they work on and the mix of data analysis and financial analysis. 

Working at the start up will allow me to interact closely with the c-suite and senior level members within the very fast growing start up. I think I will learn much more at the start up and the work is more interesting to me, but I am worried about the risks. I'm worried that I will have a hard time finding my next job or going back to school to pursue a MBA degree.  

If anyone has a similar experience, would love to hear their experience and thoughts. Or what you think in general.