Don't think of free trade agreements simply by who imports/exports more. Making free trade agreements lowers the cost of living in the country. If it didn't, they wouldn't import those items.
Although the US may ship less goods to Costa Rica than they send back doesn't make it a bad agreement. In this situation, bananas shipped are now cheaper than they were before the Costa Rican FTA, which lowers the cost of living in the US. It also creates more jobs in lower economies, helping those places. Also, since the United States has many multi-national corps, the US companies will get the profits in many instances. (for example, Chiquita gets the profits, which they in turn spend in the US)
So, the United States gets lower costs of goods, sometimes gets the profits returned, while the other country often gets more and better jobs.
You can't read any of these effects from import/export ratios, making it a flawed measure.
In reality, the perfect economic scenario for trade has each region specialized in what they can do the cheapest, and then shipping it throughout the world. Of course, heavier items are better to be made locally because the shipping costs are way higher.
IMO, it's impossible to know who wins most free trade agreements, but governments try making them because they make the world a better place. And I am happy because soon I will be able to buy bratwurst (made in the US) for cheaper!