For most Lightroom 3 users, the built-in Flickr publishing service is a solid choice. Based on the community feedback, it works reliably and integrates well if you want to manage uploads from within Lightroom.

A popular alternative is Jeffrey Friedl’s Flickr exporter, which many users recommend if you want more flexibility or prefer a third-party plugin workflow.

If you only use Lightroom for editing and don’t care about Lightroom-based publishing, tags, or library syncing, a simple export-to-files-and-upload-manually workflow is also perfectly reasonable.

One limitation noted with Lightroom’s built-in Flickr publish service is that it may not show photos you uploaded to Flickr before you started using that Lightroom export workflow.

In short: use the built-in Flickr publisher for convenience and integration, consider Jeffrey’s plugin if you want an alternative, and stick with manual export/upload if you prefer a simple editing-only workflow.