I want to create a designer workflow which is associated to particular list in all the sites. Which type of workflow I need to create? Site Workflow or Reusable workflow ?
If you want to associate your workflow to a particular list then I believe you must choose Reusable workflow.
Reusable List Workflows (Reusable Workflow) : You can create a reusable list workflow (reusable workflow) in the top-level site in the site collection, and that workflow can be made globally reusable — meaning that the workflow can be associated to any list, library, or content type in the site collection. You can also create a reusable workflow in any subsite in the site collection; this workflow is available for reuse in that particular subsite.
If you want users to be able to use the workflows you are designing on multiple sites, lists, libraries, and content types, a reusable workflow will probably best meets your needs.
Site workflows : A site workflow is associated to a site — not to a list, library, or content type. So unlike most workflows, a site workflow is not running on a specific list item. Because of this, many of the actions that are available for items not available for site workflows.
In the browser, you start a site workflow or view the status of running site workflows by clicking the Site Actions menu, click View All Site Content, and then clicking Site Workflows.
If you want to create a workflow, but don’t need a list, library, or content type for the workflows, a site workflow will probably best meet your needs. For example, you can create a site workflow as a way for people to provide feedback about your site.
For more detailed information go through Introduction to designing and customizing workflows
