What is fast file transfer?
In one sentence
Moving files between sender and recipient at the maximum speed allowed by your bandwidth, the protocol, and the physical distance — typically 10MB/s to 100MB/s for typical setups.
Most 'fast file transfer' marketing focuses on the vendor's infrastructure, but the bottleneck is almost always YOUR upload bandwidth. A 50GB transfer on a 50Mbps residential upload connection takes ~2.5 hours no matter which vendor you use — the file has to leave your computer first, and your ISP cap controls that.
Three things actually affect speed: your upload bandwidth (the cap on how fast you can push data), the protocol (TCP vs UDP-based, with FASP and similar protocols achieving 99% bandwidth utilization vs TCP's ~50-60%), and server distance (latency between you and the receiving infrastructure adds overhead on lossy connections).
For typical agency-to-client transfers (1-10GB files on residential bandwidth), most cloud services perform identically — the vendor isn't the bottleneck. For massive transfers (50GB+) or multi-gigabit business connections, the choice matters a lot.