Am I Eligible for 144 hr. Visa Free?

Well, if your itinerary is exactly like this:

Hong Kong - Shanghai - Hong Kong

This is not eligible for any kind of visa free transit because this is considered as a round trip and not a transit. However, if you have any other port call in some other country or eligigible territory between, something like this:

Hong Kong - Taiwan - Shanghai - Hong Kong

Then you will be eligible for 144 hour visa free transit and you do not need any kind of visa. The basic rule says that the immediate points before and after your Chinese destination have to be in two different countries or eligible territories (eligible territories: Hong Kong, Taiwan and Macau). Please, double check your itinerary in detail.