I'll choose to work for the first company. Here's why:

1. The news that they will go bankrupt in two years is just a rumour and there is no concrete evidence. So, they get the benefit of doubt there(Must be just a rival company trying to destabilise them). Plus, if they are a big company, I'm sure they have enough contacts to figure out how to get rid of this problem because two years is a a lot of time to get your shit together.

2. Now, let's consider they go bankrupt in two years. If I go out to get a new job and tell them I have the experience as I've worked for two years for one of the biggest companies in business before they got bankrupt, they'll hire me instantly.
   But if I go out and say I've worked for a company that had 'potential' but couldn't make it, they'll tell me I've wasted my two years.

3. Salary. $1800 + bonus and you're not gonna accept that? That too when the other option is $1200? Surely you don't have the energy and time to work extra hours worth $600 (that too excluding the bonus). Do the math.

4. Company B has potential. What is potential? Potential only means you're not there yet. And should you wait at that company till it reaches its potential? No way.
   You don't know when you're dying. I could die tomorrow. So should I waste my today working for B(potential) or A (the product/the dream).

For all those reasons, I'd choose A.