I prefer Xilinx VirtexII*, but also i use Altera Stratix (due to TriMatrix memory).
*Selection of Xilinx is 50% due to hardware and 50% due to tools.
Because we are speaking of "evolvable hardware" you can not use traditional "static" VHDL->FPGA compilers because you need to change hardware behavior "on the fly" conducted by genetic algorithms or similar, and you need a special tool.
I use my own adaptation of Streams-C FGA Compiler (designed for Xilinx devices) as "evolvable generator", this is the main reason i prefer Xilinx