I would prefer combined eSATA and USB (3.0 ideally but 2.0 is more realistic).
It needs to be able to take 2.5 or 3.5 inch drives in any combination.
Ideally it would be compatible with Clonezilla which is Linux based I believe so USB 3 docks may not work unless it would work in USB 2 mode!
There seems to be plenty of cheap units but having read reviews of the StarTech SATDOCK2UEGB which I was considering it has made me want to pay more for a recognised quality brand.
I’m also wondering how fast these will be when used for cloning when using USB as both drives will be used simultaneously! Not an issue for eSATA I presume!