The development board you linked to is for a Xilinx Spartan 6 FPGA. I have successfully used that FPGA family on a variety of projects.
Xilinx was one of the first companies to commercialize FPGAs. Xilinx has the largest market share of all the FPGA manufacturers. So if you learn with Xilinx FPGAs you will be learning what most people are using.
Xilinx currently supports two sets of development tools. ISE (which is their older tool), and their newer tool Vivado. Licenses for the full version of either tool cost thousands of dollars. But they offer a free web-pack version of their tool which supports most of their devices. When picking any FPGA you should check that the development tools are affordable.
You can get Vivado here...
You can get ISE here...
The Spartan-6 is however old technology by now. Xilinx has already moved on to the 7-series FPGA line. I believe that the Spartan-6 is not supported by Vivado. You can still use ISE-web-pack to do your development, but you won't have all the new features in Vivado.
The Spartan series is the lowest end FPGA offered by Xilinx. The XC6SLX9 is the second smallest member of that family in terms of logic cells. It contains 1430 slices. On Xilinx parts a slice usually consists of lookup tables, flip flops, and some miscellaneous glue logic. 1430 slices is only enough to support smaller projects. In contrast the 150T (the largest member of the Spartan 6 family) has 23,038 slices.
The Spartan-6 has a 6-input one output lookup-table as its main logic element.
It can achieve clock rates in the 100s of MHz range for most designs if they are implemented efficiently.
It has 18bit x 18bit hardware multipliers which are good if you plan on doing any math that involves multiplication. Specifically, you can write VHDL statements like Y <= A * B directly rather than having to build your own multiply routines from scratch.
The Spartan-6 includes 18k-bit block RAM elements which are useful for storing large amounts of data. FPGAs that do not include block rams must build distributed RAMs out of logic slice resources, which is very expensive in terms of area. The LX9 has 90 K-bits of block ram available.