Xilinx's tools are horribly buggy. And they don't want to get bug reports from you anymore unless you're a top-tier account. So their tools are a shit-show and they don't want to hear about how they can be made better unless you're already buying a lot of their parts every quarter. I don't have any experience with Altera's tools to be able to comment, but I don't hear good things from their users either.

The only way around this is to create a completely open source FPGA architecture. Most of the basic patents have expired so this should be doable now (it wasn't doable 10 years ago because too many of the basic patents were still in effect). An open FPGA architecture is the only way we're going to get open FPGA tools. You'd think that if such an architecture were created that several semiconductor companies could then produce parts.