The most cost effective choices are Enable S3 Transfer Acceleration on the destination bucket and Upload objects using multipart upload with parallel part transfers. These two approaches speed long distance uploads without requiring heavy network changes or long provisioning times.

Enable S3 Transfer Acceleration on the destination bucket uses Amazon CloudFront edge locations to receive data closer to the upload source and then forwards it over optimized AWS network paths to the target bucket. This reduces latency and can increase throughput for long haul transfers from overseas bureaus.

Upload objects using multipart upload with parallel part transfers breaks large files into parts and uploads parts in parallel which increases throughput and reduces the impact of single part failures because you can retry individual parts rather than the whole file. Multipart upload is simple to implement and is very cost effective for tens of gigabytes or larger objects.

Provision AWS Direct Connect links from the overseas offices to AWS and send uploads over them is not the best choice because Direct Connect requires physical circuits and can be expensive and slow to provision, so it is not cost effective for rapidly improving uploads from many distributed teams.

Configure AWS Site-to-Site VPN tunnels from overseas offices to a VPC and route uploads through the VPN is focused on VPC connectivity and adds IPsec overhead, and it does not provide the edge ingestion and optimized public paths that accelerate S3 uploads, so it will not reliably speed large transfers.

Use AWS Global Accelerator to front the S3 bucket for faster uploads is incorrect because Global Accelerator does not support S3 as an endpoint and it is designed for accelerating traffic to ALB, NLB, and EC2, so it cannot be used to accelerate direct S3 uploads.

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