Im planning on buying the HD5850,
and the Asus one is a bit more expensive,
are there any significant differences between them both?
and what is the recommended one of those?
The Asus has Voltage Tweak - allowing you as standard to increase GPU core voltage to help make OCing easier and is one of the very few to offer this currently I understand.
I also think the Asus card doesn't have a CCC overclock limitation. That being said, unless you plan on heavily OCing the card there is negligible difference.