bettervoting.com is run by the best-funded STAR advocacy organization, so on that basis alone is the best bet for the future.
“It’s always something”, though, so best to work out kinks early.
From my quick exploration, it appears to offer “almost everything” we want: multiple-winner “bloc STAR” (although not under that precise name), and the ability to download anonymized ballots (in either JSON or, much smaller, CSV format).
But … as someone who created a test election, is the ability to download anonymized ballots unique to me? Don’t know. And so on. Many questions will arise.
Helios made a ton of “security promises” so extreme that Helios never saw a raw ballot to begin with. Your ballot was encrypted before it left your browser, and in theory not even Helios could decrypt it. Very few other services are that … cautious.
Helios allowed changing your ballot at any time before the election closed. This service appears not to. But I’m not sure yet. I don’t really care. Do others?
Ties here are resolved by a randomized algorithm. It’s unclear whether that’s deterministic across separate runs. Larry’s library has a bunch of ways to handle that. If people care (I don’t, much), we could do the scoring ourselves. Larry’s library supports ways that are deterministic.
For a “restricted” (not open to the public) election, you can supply a list of email addresses of voters, or “IDs”. The latter are apparently gibberish strings you make up and pass out to voters. If someone goes to the site and can type in one of the pre-approved gibberish strings, they can vote; else they can’t. Which do people prefer?
One repeated annoyance falling on whoever creates the election: the process seems plodding. There’s not just a page of options to select, but many little areas to interact with. You start by clicking a radio button picking between “election” and “poll”. And that’s the only thing you can do at first. Click “election”, and then you have to click a “Continue” button to activate the next box: “What’s the title for your election?”. 3 “Continues” later and the initial page vanishes, and then you’re left wondering what to click on next.
It wasn’t then clear to me how to add a list of candidate names. That’s done by clicking the “Add” button to the right of “Races”. Their mental model is apparently that “an election” can consist of multiple “races”. Common in real-life political elections, but no so much in PSF elections.
And so on.
Absolutely. I know almost all “the right options” to pick here, but if you’re creating the election, you’ll have to wrestle with the UI. Practice early & yell “help” often 
Of course I’ll be happy to participate in any test elections people may want to create.