That would depend on what type company. If it is import/export there can be some advantages to being in Hong Kong. I have lost the link, but recently read an article about the requirements for foreigners wanting to register a company in the PRC is getting lowered. It is not uncommon for companies to register both in Hong Kong and PRC. Any trade with the rest of the world is done through Hong Kong and the majority of work would be done in PRC. 

Note. You can register a company in Hong Kong without having any presence there. You are required to have a mailing address but you can buy that as a service.

The question is too generalized for anybody to be able to answer accurately. There are many factors that could affect the decision. You need to look at your business plan and the key objectives. Then do some research as to which gives the best benefits. I suggest not relying too heavily at this stage on agencies to provide advice. Most of what you need is freely available and not worth investing in. However, once your initial decision has been made, it could then be worth seeking professional advice because pursuing businesses anywhere in Asia can be fraught with danger (and conversely opportunism).

Regardless of where you register it, you still have to pay income taxes to Uncle Sam.. So you might as well register it back in the USA, assuming that's your home country.

It probably wouldn't be wise to try to register a company abroad without registering it in your home country these days because there's a big crack down on people who are registering shell companies in other countries to hide their money from the government's tax agencies to illegally evade taxes. Now is probably not a good time to register a company in a foreign country as everybody doing so is being strongly investigated for tax evasion.

I've got two companies/"doing-business-as" that I need to register with my county in the USA (don't need to register for state/federal because no employees). It's a PITA because I'm from a small town that still does everything with pencil and paper and they don't even have the forms online. Don't even get me started with the NYS DMV and trying to get my driver's license renewed while abroad :(. /rant.