Of the OpenID providers I reviewed (see the posts in their full glory:  Chi.mp, Verisign Personal Identity Portal [and an Update], Your Internet ID (YIID), MyOpenID), here’s my opinion on them (one being best, four being the worst)

Trustworthiness:

1. Verisign Personal Identity Portal
2. MyOpenID
3. Chi.mp
4. YIID

Options/Features

1. Chi.mp
2. YIID
3. Verisign Personal Identity Portal
4. MyOpenID

Ease of Use/Simplicity

1. MyOpenID
2. YIID
3. Verisign PIP
4. Chi.mp

It is worth noting that the available features (a lot vs very few) directly affects the ease of use as more features take more time to learn.  As for the trustworthiness, it’s based mainly on reputation- Verisign is known for providing security certificates to sites and offers a multitude of verification options.

My personal favorite is Chi.mp because in addition to providing an identity it gives users their own home on the Internet with its own domain name and importable content.  This may not influence those who already have a web site (and who can, by the way, use it as an OpenID URL), but for those who are strewn across the Internet across many networks, it pulls them all together.