What Are They?
The Paris Convention was drafted to allow individuals to file a patent in their own country first, and there is a twelve month period after this initial date where you can file elsewhere. This gives patent holders time to perfect their product, seek funding, and do more customer research to make sure that there doesn't need to be any changes. The Paris Convention prevents inventors and entrepreneurs from having to file patents simultaneously in all the countries that he or she wishes to, which can be overly complicated and very costly.
The PCT allows inventors and entrepreneurs to file in their home country first and enjoy protection elsewhere too, but there are a few differences that must be pointed out. First and foremost, the PCT is generally more expensive than direct national filing. That's because when you use PCT filing, you're basically filing a patent in every PCT country. You also get more time than you do for the Paris Convention direct filing system. In most countries, your rights are retained for 30 months.
Which One Should You Choose?
This will depend on the type of patent you have, how confident you are that it will hold up, what your financial situation is, and what industry you're in. For example, if you're in an industry where there are constant changes, that extra time with PCT filing may be useless. At the same time, though, PCT can save you a lot of hassle if you plan on filing in a number of different countries. However, if you're only going to file in a few, direct filing may make the most sense. Also, there are some countries that are not PCT, so this must be taken into account as well. It may be a good idea to speak with professionals in patent services to determine the best option for you.