Camel's API is smaller & cleaner (IMHO) and is closely aligned with the APIs of JBI, CXF and JMS; based around message exchanges (with in and optional out messages) which more closely maps to REST, WS, WSDL & JBI than the UMO model Mule is based on
Camel allows the underlying transport details to be easily exposed (e.g. the JmsExchange, JbiExchange, HttpExchange objects expose all the underlying transport information & behaviour if its required). See How does the Camel API compare to
Camel supports an implicit Type Converter in the core API to make it simpler to connect components together requiring different types of payload & headers
Camel uses the Apache 2 License rather than Mule's more restrictive commercial license