As far as traffic is concerned, I've actually noticed a small (not yet very significant) improvement in traffic in the past few weeks after a big slump earlier in the year, though whether this is due to 'Editor's Choice' is not easy to evaluate. Looking at weekly visits to my hubs, there's no clear effect - all my Editors Choices are evenly distributed among the other hubs.
Since Editors Choice came in, my hub scores and hubber score have both risen very appreciably, which is one really nice aspect, as it signals an endorsement of one's writing for which I'm grateful, though that of course doesn't necessarily translate into increased traffic.
I personally cannot see any reason to opt out. Whether there is any traffic increase / financial advantage to having Editor's Choices, I can't say for sure, but it's certainly nice to think that maybe the hubs are being reviewed by human beings on the HubPages staff rather than just some sort of unintelligent algorithm. I'm sure this can only be a good thing.