It’s really easy to just select farm solution for your Visual Studio project:

That’s your choice provided that your IT department doesn’t mind or your customer doesn’t know any better.

But, if they do care about security, they may insist that you find a way to meet the requirements of the solution while staying in the sandbox. Trying to convince a savvy admin or an IT director that your application must be able to run at full-trust may fall on deaf ears.

A better approach to take is to identify exactly what pieces of the api you really need and offer the option of a hybrid solution. A hybrid solution allows you to develop a proxy that can expose classes to your sandboxed solution that would otherwise not be allowed. The proxy will have to be a full-trust solution. However, allowing one full-trust solution to execute in an effort to potentially keep several other applications in the sandbox is a much easier sell than doing all farm solutions all the time.