As I said, the easiest way, fastest and one of the cheapest way to get the Chinese stamps is to take the KCR East Rail. HK$33 from Kowloon to Lowu ($36.5 from the new TST-E). Takes about 40 minutes (depending on where you get on).

The ferries are much more expensive from Kowloon to Shenzhen (Shekou) or to Macau. [HK-Macau is about HK$140 weekday, Kowloon-Shenzhen is about $190, both each way].

Other cheap ways to get to China is by bus, but more complicated than taking the KCR East Rail trains.

Anyways, if you're going to Macau, the First Ferry vessels from Kowloon are also jet-propelled, just that they are catamaran type with no foil. So, they are still suspectible to wakes. The Turbojet service from Hong Kong Island use 3 types of vessels, and you don't get to choose - you may get a jetfoil, a catamaran (called the Tri-cat) or a foilcat. Since they have more jetfoils than other types, you have the greatest chance of riding one, but a Tri-cat or foilcat is also possible. All take about 55 minutes. First Ferry's are a little slower, so maybe 60-65 minutes.