Afaik Wriggle's is rng, and thus, very unpredictable.
The Spirit items add a steady damage increase to all of your attacks to any jungle creep. I'd say it's far better than Wriggles, but it also comes at a higher cost. This is why it can be preferable to rol with Wriggles on Vi since you really want to get your BC/FM asap. However, you can also decide to just upgrade your machete to a Spirit Stone, and upgrade it later during late game. It'll also give you a true damage dot which I'd say is a safer source of steady damage over Wriggles.