Harilal, if by best u mean the slowest of the 3, than yes 5670 wins.
The 4850 and the 250GTS are both faster than the 5670, and by a descent margin.
THe 5670 is not without merrit, its a very short card, and doesn't require and extra power connector, so it sucks in a good clip less power than the other two (less strain on the psu). It can also do DX11, but at the performance level, it might as well not.
The 250GTS is marginally quicker than the 4850, and sucks marginally more power, in retrun the 4850 supports DX10.1 vs the DX10 for the 250GTS.
Whichever is a cheaper, thast the one I would get out of the two. If you have a weak PSU, u might consider the 5670, otherwise skip it.