Going against a worlds deck does offer practice. However, other lists are better for specific reasons.
For example, I would DEFINITELY put any of my lists up against yamato's magma deck, because it is still widely usable for this format. In his entire list, all you have to do to make it rs-on is -3 underground expo, and +3 anything else. Magma is also a deck to fear still, so this is one of the first things I put my decks to the test against.
I "might" put Chris Fulop's blaze deck up against some of my things. However, several pivotal searching and 1-copy cards, like PETM, oracle ,friend ball, and town volunteers, are no longer available in this format. These things make his list what it is, and without them it isn't accurate enough. Fortunately, it is blaziken, and is good testing foundation because the archetype itself is still popular.
Kevin Nguwen and Reed Weichler's Gardevoir and Swampert decks aren't worth testing most of the time. They are okay, but not qualified enough to consider for testing, especially since gardevoir and swampert aren't metagame factors.
However, no matter which list you are using, try playing the roles of BOTH players, and don't just settle for getting your little sibling or w/e to play it. You get two times the practice if you have to think for two different people!
