2Tb Hdds: 2¾" Or 3½"?

[gl556tr]

I am looking for a pair of HDDs with a capacity of ≥2TB, then pop them into an external enclosure with RAID 1. Then second similar enclosure for a secure backup.
With 2¾"-HDDs now offering such capacities, is there any advantage/DISadvantage is choosing this over 3½"? Certainly, for the latter there would be less energy=heat-generation.
(Less important, but intersting: more and more have 3TB - so go for them if price & maker is good?)

[VHG]

Smaller "laptop type" hard drives tend to spin slower then larger "desktop" hard drives.

Laptop drives spin at about 5,400 and dekstops spin at about 7,200.

So far better to go for desktop hard drives (3.5 inch).

[carrust]

The op is all Klingon to me:-)

[ChuckFickens]

Then why bother answering it?