Hello @sktv , first of all I want to thank you for reading my post, and for your valueable comments...
Anyways lets come to the points..... defining best graphics card for GPU mining is very tough....
but you can think about bellow mentioned few graphics card that is most popular nowadays...
NVIDIA GeForce GTX 1060/1070
AMD Radeon RX 570/580
AMD Radeon RX Vega
Nvidia GTX 1080 Ti
Nvidia GTX 1070 Ti
AMD Radeon R9 295X2
etc.....
and lastly I want to say if these information give you little bit idea please don't forget to let me know using commets....