Enterprise Service Bus Vs Hub-and-Spoke

The nature of the ESB is distributed; ESB is more scalable than the hub-and-spoke architecture. With ESB the ability to deploy separate integration services, scaling up and scaling out becomes easier.
An ESB is based on open standards. EAI/hub-and-spoke solutions are generally based on proprietary standards.

Advantages of the ESB architecture over the hub-and-spoke architecture are:

Hub and Spoke

• Centralized architecture.
• Central point for availing services like transformation, routing and transaction management.
• HUB (message broker) is a monolithic piece of software.
• Capabilities of the HUB cannot be used as pluggable components in another HUB.
• Services provided by the HUB and the interfacing between these services is not standard based and is usually propriety standards driven, leading to a risk of vendor locking.
• The hub, being a monolithic piece of software can be used only in a ‘all or nothing’ mode.
• Complicated operations, such as package sorting and accounting, can be carried out at the hub, rather than at every node.
• Spokes are simple, and new ones can be created easily.
• Scheduling is convenient for them since there are few routes, with frequent service.

Enterprise Service Bus(ESB)

• Distributed and more scalable architecture.
• Central point for availing services like transformation, routing and transaction management.
• ESB provided services are themselves distributed in the sense that different components come and play their role in providing the infrastructure services promised by the ESB.
• Specific capabilities of an ESB can be plugged into other ESBs to allow the user to get the benefit of mix and match of services.
• Services provided by ESB, deployment and installation of these services and interfacing between these services is standard based.
• ESB user can choose which services need to installed and used which services they want to leave per instance of the ESB.
• Faster and cheaper accommodation of existing systems.
• Increased flexibility; easier to change as requirements change.
• Standards-based.
• Scales from point solutions to enterprise-wide deployment (distributed bus).
• Predefined ready-for-use service types.
• More configuration rather than integration coding.
• No central rules engine, no central broker.

references:
http://en.wikipedia.org/wiki/Enterprise_service_bus
http://software.intel.com/en-us/articles/soa-esb-what-is-all-this/
http://dotnet.sys-con.com/node/121831?page=0,0