Assuming eSATA 150, it’d be 150 MB/sec.
USB 3.0 theoretically maxes out at 625 MB/sec, but that’s just raw data.
This article gave a bit more explanation (USB has to encapsulate or translate the data) and real-world measurements.
USB 3.0 vs eSATA - is faster better? at ITWorld.com
With eSATA, you have point-to-point connection (though you can hub eSATA, it quickly gets unwise).
With USB, you have a hubbed connection and more overall bandwidth, but you also may have many more devices sharing that bandwidth.
For a single device, my preference, when it works, is eSATA because that’s a dedicated-to-storage connection.
I say “when it works” because not all SATA controllers support the port-multiplier function (multi-LUN) that is needed.