USB3 or eSATA for external drive

Hello!
I just bought an SSD for my laptop, and I would like to use my old HDD as an external drive, but still install programs there (those that require low bandwidth).

After installing the SSD I noticed that my laptop internal drive interface is SATA2 and not SATA3 as the SSD, so it's not running at full power but still a lot faster than before. From here I found out my HDD is SATA2 as well.

Finally, the question: I have a UBS3 port and a eSATA/USB2 port on my laptop, which one should I use to get the fastest operation from using my old HDD as external drive?

Thanks!