Any graphics card with a PCIe x16 interface would be compatible with your Z97 motherboard. The main factor in deciding which GPU to buy is your monitor's resolution/refresh rate that you are gaming at.
A GTX 1060 (or RX 480) would be good for 1080p/60Hz gaming. A GTX 1070 would be ideal for 1440p/60Hz or 1080/120Hz+ gaming (especially if you have a G-Sync monitor).