which one to choose: E7K60 or 7K60?

The E7K/60 is designed for server 24/7 use.

It is not designed for power conservation or extended start-stop service - in other words, NO. Use the 7K60 for notebook use and the E7K60 for blade servers.

then?

can it be used in a laptop?

Not to contradict the above poster but the "E" version can be used in a laptop as it has the same physical dimensions of the non-E version though its use in such an environment is not what it was made for and therefore not recommended.

I don't think the E version is cheaper, when I have looked it's more, and I can't say I have noticed a big difference in speed over the 5400 drive, you could be better off with more space if your buying a new drive