I think OpenLayers is the best. You can easily make WFS calls to an WFS service.
If you want to just return data and not map features, you can also do this. Or map features without the data, or both.
here are some examples:
You should be more precise and tell us if you want to use returned data or map features.
See capdragon answer regarding map features. If you only want to handle data, the following can be a good & light alternative :
If you want to parse a GetCapabilities WFS server response, you can just use jQuery because it's xml ( http://marcgrabanski.com/articles/jquery-makes-parsing-xml-easy ). You could also implement jQuery invoking GetFeature since output is xml/gml formatted