Should I join a post Series B startup

I have three offers Dropbox, SF - TC ~450K as an EM AutoDesk, SF - TC ~230K as an EM Startup, LA - TC ~180K (plus 100K equity/year) as a Dir of Eng. Now I am mostly lingering between Dropbox or the start up. Even though the start up is paying less cash their equity is pretty decent with a good upside if they have a good exit. Now this is where I am a new bee in terms of start up maturity levels. So I did some research and below is what I know about this start up and I need some guidance from people who are working with start ups. For extreme anonymity reasons (a bit ironic though) I'm not naming the startup. About the start up They are an E-Commerce company competing with Amazon, Walmart and Costco within a niche vertical. Year 1 - Self funded and kicked off the company Year 2 - Raised $7.5M in Series A with $50M in Sales. Year 3 - Raised $120M Series B, with a valuation of $600M, sales at $100M Year 4 - Sales around $150 to $200M Year 5 - Sales at $200M Year 6 is 2019 Burn rate is ~$20M/year. When asked if when they are planning to raise a Series C they said that they are not looking to raise a new round at least for the next 2-3 years. Overall, as I am trying to dissect this it feels like a pretty matured growth company that could have a decent exit in the next 3 years. However they are not profitable and are planning to be profitable by 2020. Worst case I will be left stranded with their equity which may not mean anything unless they have a good exit. Their team on paper and track record looks solid and their offer matches with my current base. What do you think? Any guidance or suggestion would be very helpful. Thanks in advance.