Depends what your trying to do. E-coining? Hell yes AMD. Want 120Hz, hell yes NVidia. Etc.
What do you plan to use the cards for, gaming? What games? Then do a simple google "the game name" benchmarks and see where each type of card stacks up on it and what settings they recommend. DO REMEMBER, it isn't ALL GPU anymore, so if your on a A8-5000K or Intel Duo Core Duo, neither will help improve your gaming performance on BF4, the CPU and being on DDR2, etc. all will still IMPACT the playability. You need to match the card performance across a standard PC (7200RPM HDD or SSD, SATA III, DDR3) and proper CPU (FX-8xxx or i5 / i7 -4xxx are the standards for gaming) and have a proper PSU to be able to support any Video Cards added (off the shelf systems are between only 245w-300w). .