Assuming all 3 made equally attractive offers, I'd go with Company C and get a good mix of cash and stock and the promise that there's a path toward running my

Assuming all 3 made equally attractive offers, I'd go with Company C and get a good mix of cash and stock and the promise that there's a path toward running my own department or division. The hope is that if and when the company makes it to IPO or another liquidity event, I'll be in a good position to take a good portion of the credit for that success, as well as the monetary upside. I figure company B is what you're leaving and since Company A is in a space that is hard to monetieze/productize (according to the OP they are similar to the idea he has), there may be a long road ahead for them.