Satwika,
Each product has it's own uses for specific needs, so here's a rough outline of what you've listed to help you get started:
Bing Map AJAX Control - client side javascript for displaying map and map interaction
Bing Maps SOAP Service - server side interaction for displaying map, back-end geocoding and routing, getting static images. Use if you need more control over geocoding/routing/imagery than what is provided out of the AJAX control.
Bing Map REST service - lighter and faster version of the SOAP Service
Bing Spatial Data Service - Batch geocoding process
Mappoint Web Service - Older version of the Bing Maps SOAP Service (acts very similar) - you can start with an evaluation account which allows around 10,000 transactions/day and move to a contract/production when you need to. Overall I'd just
move to the Bing Maps REST Service or AJAX Control because the functionality is very similar but data + performance is better.
In short, just stick with the AJAX version, and then use the REST service when there's some specific geocoding/imagery needs that you have.
Hope that helps,