Schema.org or Data-Vocabulary.org for breadcrumbs?

Yes, avoid Schema for now and use Data Vocabulary, for exactly the reason you cite. I've used the latter, and it works.

John Mueller from Google has said that he expects Schema will have to change, and the discussion around it seems to suggest that Schema needs to be more like the current Data Vocabulary syntax, so any future adaptations you need to make may be less onerous than they currently appear.

Up-to-date answer, January 3rd, 2017

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data-vocabulary.org - offers microdata for breadcrumbs for quite some time now. Simply use it like this:

  <div class="breadcrumb">
    <span itemscope itemtype="http://data-vocabulary.org/Breadcrumb">
      <a href="http://www.contoso.com/" itemprop="url">
        <span itemprop="title">Contoso</span>
      </a> »
    </span>  
    <span itemscope itemtype="http://data-vocabulary.org/Breadcrumb">
      <a href="http://www.contoso.com/fashion/" itemprop="url">
        <span itemprop="title">Fashion</span>
      </a> »
    </span>  
    <span itemscope itemtype="http://data-vocabulary.org/Breadcrumb">
      <a href="http://www.contoso.com/fashion/women/" itemprop="url">
        <span itemprop="title">Women</span>
      </a> »
    </span>
    <span itemscope itemtype="http://data-vocabulary.org/Breadcrumb">
      <a href="http://www.contoso.com/fashion/women/boots/" itemprop="url">
        <span itemprop="title">Boots</span>
      </a>
    </span>
  </div>

read the docs

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schema.org - also offers the use of microdata for breadcrumbs! Simply use it like this:

  <ol itemscope itemtype="http://schema.org/BreadcrumbList">
    <li itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem">
      <a itemprop="item" href="https://example.com/dresses">
      <span itemprop="name">Dresses</span></a>
      <meta itemprop="position" content="1" />
    </li>
    <li itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem">
      <a itemprop="item" href="https://example.com/dresses/real">
      <span itemprop="name">Real Dresses</span></a>
      <meta itemprop="position" content="2" />
    </li>
  </ol>

read the docs

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GDav: "John Mueller from Google has said that he expects Schema will have to change, and the discussion around it seems to suggest that Schema needs to be more like the current Data Vocabulary syntax, so any future adaptations you need to make may be less onerous than they currently appear."

Well I guess they changed, because now schema.org also supports breadcrumbs.

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Please note: both data-vocabulary.org and schema.org use microdata for search engine optimization. Apperently there are ways to combine them, but I haven't found a live example, so if I were you I would choose one of them. And then use it for all your content (I mean that I wouldn't use data-vocabulary for your breadcrumbs and schema.org for your navigation menu).

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Conclusion:

They both work, just choose one.