Which coin are you talking about?
There's no GPU that is good for mining Bitcoin. Nothing will earn you any profits whatsoever. You need an ASIC such as the Antminer S9.
For Ethereum, which is most likely the most common GPU-mined coin right now, the best GPUs are the RX 500/Vega series.
For more information/other coins, you're better off asking here:
https://bitcointalk.org/index.php?board=160.0