Hosted GET or PUT from external system?

We have an external system using Oracle and a REST web service. We want some of the data in that system to be accessible in a data source on Forms On Fire. We know there are a couple of methods to doing this so we want some advice on the best way to do it, along with pros and cons. 

1. Hosted GET. We can create a data source that uses a hosted GET to bring new data into a data source every 15 minutes. What are the limitations of bringing data into the platform with this approach? Do we only need to build a REST web service with a GET method for this approach? How do we ensure the web service on our end is not open to malicious attacks? Can this data source be updated by a form?

2. Build an external process that performs a POST into the platform. With this approach, we think that we need to create a program/process that takes any new data from our system (a table for example) that will POST those new records as they appear in the table into a data source on the platform. What are the limitations of doing this? Is this the correct approach? Using this approach, will a data source be "user defined" and allow updating by a form? 

Thanks for any help you can give to me. 

Victor