We use OpenNLP in production and it is very stable/robust (though, not exactly cutting-edge anymore). We regularly push large corpora (e.g. German Wikipedia or 20 years of newspaper text) through some OpenNLP-based services, without any problems. This in contrast to some other tools, which I won't name, that have horrible concurrency issues, etc.

It would be helpful if you named the other ones -- always useful to hear examples of what works and doesn't.