Utility vs Design Patent as fast mean to secure IP rights

Question

I want to apply for a regular patent of a simple static mechanical device (no moving parts). It's design is dictated mostly by its functionality. Most changes to the physical appearance of the device will annihilate it's functionality. I want to apply via PCT in several countries, most important of them - US and China. I plan to submit a provisional patent application first.

As a complementary measure, to secure some basic IP protection fast, I would like to simultaneously apply for utility and/or design patent. My question is - which of them should I choose in my case(/or maybe both)? I.e.:

1. which of them is faster/easier/cheaper to obtain and maintain?
2. can a provisional patent application secure priority right for utility patent and design patent the same way it does for regular patent? And if not - may I loose the right to obtain one of them by a public disclosure with a PPA only?
3. what constitutes infringement of a design pattern? E.g. simple scaling of the size is probably an infringement of both - utility and design patent, however if somebody changes proportions of my device by making it longer than the original and it still will function in the same way - it is probably infringement of utility patent but no longer of the design patent - correct? And if it is still not an infringement of design patent - how substantial a deviation from the original design should be to constitute an infringement?
4. is there any advantage to maintain them once a regular patent is granted?

Answer 1

1. A US design patent is less expensive and much quicker than a typical US utility patent. The European counterpart (Community Design Registration) is easier and faster and with no examination. However “Most changes to the physical appearance of the device will annihilate its functionality” rules out protection based on its “looks”. Functional aspects are specifically not covered in theses systems.You could add some graphics to it and get protection for that but a copier just makes it plain. Also “can a provisional patent application secure priority right for utility patent and design patent the same way it does for regular patent?” was pointed to in a comment. A utility patent is what people might call a “regular” patent. An aside - some countries do offer a “utility model” that is a regular patent light. A U.S. provisional can be used as priority for those.
2. Moot for you but for future readers, no a PPA can not provide priority for a US design patent. Design patent fees are quite low and the application depends on very precisely drawn figures that would need to be specially created and usually found in any other type of application. (For completeness - there is a very little used process that could let the contents of a PPA provide priority to a design patent in the very unlikely situation where the application originally filed as a PPA contains suitable drawing.)
3. Again moot for a device whose function comes from its form and has no ornamental aspects. Infringement is based on first comparing your granted design patent to what came before it and then comparing it to the alleged infringing device. If yours is a great departure from the past and the alleged infringer is very close to yours then it is likely infringement.
4. Design patents and utility patent protect different aspects. Apple vs Samsung was worth millions of dollars due to similar overall look, aspect ratio and particularly the radius of the corners of their respective phones. It had nothing to do with the function/utility of either phone. Another factor in answering this is there are no maintenance fees for US design patents so once granted there is no cost to keep it in force. That is not universal worldwide.