data-attribute or Class selector

How do you prefer to author your markup when adding a new filter?

``` html
<div class="MyClass" data-filter="Eureka"></div>
```

or 

``` html
<div class="MyClass filter-Eureka"></div>
```

I'm thinking of using `data-filter` mostly because: Filters can't be mixed together and only one at the time is allowed. `data-filter="Eureka Karl"` wouldn't work.
