The first criteria in selecting a SPI flash is density. For many designs this means selecting a flash device that is large enough to store the configuration bitstream of the target FPGA. For some designs, other considerations narrow the options of which flash to use, such as the need to store multiple bitstreams, or have a daisy chain of FPGAs to be configured, or configuration speed.
The minimum density required is always the size of the FPGA configuration bitstream. See UG470, 7 Series FPGAs Configuration User Guide for details. If the design requires multiple bitstreams, multiply the size of the bitstream accordingly. The Xilinx tools allow bitstream compression, however it is not recommended to rely on compression when determining SPI flash size because compression varies greatly with the user’s design and is not predictable.
Some designs require the FPGA to configure in a specified amount of time. In this case, the designer should consider using a SPI flash that allows for the fastest read-clock rate and ensuring the support of x4 data width read operations (sometimes called quad output fast read in SPI flash data sheets).
The designer also must consider the I/O voltage compatibility. The Artix™-7 and Kintex™-7 families support configuration I/O voltages up to 3.3V and the Virtex®-7 family supports up to 1.8V. The SPI flash vendors generally use the same voltage supply for the core voltage and the I/O voltage. However, some vendors can use a separate I/O voltage pin. The differences in the type of voltage supplies affect the ability to use different vendors as a second source. See XAPP1328, Configuration or Boot with NOR Flash for Sourcing Flexibility and Cost Reduction Application Note.
The list of the flash devices that are tested and supported by the Xilinx Design Suite tools for the 7 Series families can be found at ISE Design Suite:
https://www.xilinx.com/html_docs/xilinx14_7/pim_r_supported_spi_bpi_proms.htm
See UG908, Vivado Design Suite User Guide: Programming and Debugging for a list of supported devices.