The best replacement for xilinx is altera.

The best alternatives to xilinx are rated as following:
★★★★★  altera
★★  lattice
★★  actel
★★  quartus
★  altera fpga
★  intellectual ventures
★  modelsim
★  altera cpld
  atmel
  alterra

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Speaking about xilinx, one probably shouldn't forget about modelsim.

Other search terms related to xilinx and their ratings are:
★★★★★ modelsim
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