xilinx FPGA
I'm not sure what you mean by "best".
I suggest starting with Xilinx ISE 8.1i. It includes all the tools you need. The WebPACK version is free, but it supports only the smaller FPGA devices. The full-featured Foundation version costs about $2500 US.
You can use the HDL compiler included with ISE. It's called XST, and it works pretty well, but some folks prefer Synplicity Synplify Pro. It's expensive, around $19000 US.
ISE includes ModelSim XE, a light "Xilinx Edition" HDL simulator. The full-featured ModelSim SE is much faster, but costs around $20000 US. ISE also includes its own built-in "ISE Simulator", but the previous version was simply awful, and I haven't tried the 8.1i version.