1f56bc31_ox_vs_App___SharePoint_Dragons__Farm
[0] Safety [Sandbox] Very safe. [Apps] Apps rely on OAuth 2.0. The OAuth 2.0 standard is surrounded by some controversy (for example, check out what OAuth lead author Eran Hammer has to say about it here: http://hueniverse.com/2012/07/oauth-2-0-and-the-road-to-hell/ . In fact, some SharePoint experts have gone on the record stating that security for Apps will become a big problem. We’ll just have to wait and see how this turns out. [Farm] 
Can be very safe, but this requires
SharePoint 2013: What to do? Farm solution vs Sandbox vs App | SharePoint Dragons
Farm