Pre-existing arguments when using queries

Question

I am struggling to understand how queries work with get_posts(), query_posts() and WP_Query(). In particular I do not understand what pre-existing selection may exist when using these on a given page template. From various blogs it seems that the default situation is that query_posts() and WP_Query() apply any pre-existing filters whilst get_posts supresses them. However the codex says query_posts() ignores other parameters it receives via the URL (such as page number or category.) Are these filters / parameters the same or something different? How can I definitively tell what pre-existing selection will exist when I create a query?

Answer 1

When should you use WP_Query vs query_posts() vs get_posts()?