JAX-RS Implementations

Jersey

• Reference Implementation
• Usually the most cutting edge
• Supports true asynchronous (ie web sockets etc…) connections through either Atmosphere or 2.0 version.
• Has support for Spring and standard injection containers (ie @Inject).
• Glassfish bundles it.
• Its much more modular than the other JAX-RS projects.
• It has a kick ass URI Builder
• Does not necessarily require servlet container.
• Grizzly support
• Netty support (very early).
• Swagger support
• Sort of missing OAuth 2.0 . You’ll have to use other libraries.
• Some MVC support through Viewables
• Hosted on java.net (a minus as the site is terribly slow at times).
• Licensing is based on CCDL 1.1 and GPL-v2. Please make sure you check Jersey licensing before you use it for commercial use

https://jersey.github.io/license.html

RestEasy

• Much of the above but most notable supports view technologies (see HTMLEasy)
• It does have asynchronous connection support
• Cache support
• EJB support (if your into that crap)
• JBoss bundles it (I think)
• Netty support
• Arguably the best Spring integration (MVC handler).
• Early Swagger support
• More security support including early OAuth 2.0 support

Apache Wink (never used it)

• I have no idea why this project exists.
• Supposedly its high performance focused.
• It has a client built on top of HttpUrlConnection (which is a minus… it should be pluggable like Spring RestTemplate).
• Basically Wink was developed in house at some enterprise companies and then given to Apache.
• Requires a servlet container.

Restlet

• Very powerful but very complicated
• Provides some low-level REST support
• Does not require a servlet container

Apache CXF

• Some interesting WADL support.
• Reuse and or combine JAX-RS w/ JAX-WS
• Security support
• Integration w/ Spring albeit kind of nasty
• Supposed Autogeneration of client stubs

Other RPC-like systems

Message Queues

• RabbitMQ
• ActiveMQ

Asynchronous RPC

• Finagle — from Twitter.
• msgpack-rpc

My humble opinion

I know the OP asked for REST but if this is for internal communication seriously consider using either a message queue or some other asynchronous RPC (Finagle) instead of traditional REST if your requirements match those systems.

If it must be classic HTTP REST (external) I would choose between either RestEasy or Jersey as a bulk of the mind share is put into those two projects.

Also see: Rest clients for Java?