atmosphere is really the best i've seen (i haven't used any, but i've evaluated multiple solutions). the good thing with it is that it uses the best mechanism available. if running on servlet 3.0 - using the async support. if using jetty - using its support, and so on. it also has spring integration.
so, perhaps you should ask a concrete question about atmosphere. see this and this related questions.
atmosphere is really the best i've seen (i haven't used any, but i've evaluated multiple solutions). the good thing with it is that it uses the best mechanism available. if running on servlet 3.0 - using the async support. if using jetty - using its support, and so on. it also has spring integration.
so, perhaps you should ask a concrete question about atmosphere. see this and this related questions.