According to this post it's not possible to use Craft 2.x with Amazon S3 within the Frankfurt region. As Craft 3 is still not near release it would be nice to have some sort of a fallback solution. For us that issue is a major drawback ... and I can imagine for other folks from the EU region too.
The AWS Frankfurt region (eu-central-1) does only support the "new" v4 signature. Craft 2 uses the v2 signature of the S3 API and that's not easy to fix.
Ireland (eu-west-1) should be good enough in terms of latency.