Which of the following Graphics is best ??

Bro, the core clock is important, but the ARCHITECTURE is MUCH more important.

Lets compare it to cars – 3 engines, all rev to 8,000 revolutions per minute, rpm. Are they equally powerful? NO. They have 4-cylinders, 8-cylinders and 12-cylinders, respectively.
So, even if the 4 cylinder revs to 8000, 4 cylinders are weak.
But 8 cylinders going at 8000 is fast, and 12 is INSANE.
Get me? = )

So, Assume the 5770, 5850 and 5870 all have the same clocks, ok? BUT THEY DON'T HAVE THE SAME ARCHITECTURE.

CARD Config Core (Unified Shaders: Texture mapping unit: Render Output unit)
4890 800:40:16
5770 800:40:16
5850 1440:72:32
5870 1600:80:32

So you see; the 5870 is the most powerful; it is EXACTLY TWO 5770’s.

Now, the 4890 seems the same as the 5770, but it’s not. It’s not just the Configuration Core that determines how good a card is, it’s a few other things; one of them is Bus Width (which is measured in BITS); the 4890 is made on a 256 bit bus, but the 5770 is made on a 128 bit bus.
So purely based on gaming performance, which renders more frames, the 4890 is more powerful.
BUT, the 5770 has NEWER Architecture, so u can plug it to 3 monitors, it can run DirectX11 and it consumes A LOT LESS POWER, therefore less HEAT, so it’s less NOISY.

The 4890 consumes 60 W when idle and 190 W at maximum.
The 5770 consumes 18 W when idle and 108 W at maximum (almost half the 4890).

So, YOU must decide which is better, depending on what your criteria are. Overall, the 5770 is the better product, but the 4890 is a little more powerful form a purely gaming perspective.

Good luck.

Peace.