When I want to add a contact,should I add it my gmail account or Phone-Cloud account? What's the difference? Pros? Cons?
I like the gmail (Google) option.
They will always be with your Google account and you can even access them on the computer through gmail.
also if you ever switch carriers they will still be with Google.
The Google contacts have worked for me since 2009 through two carriers and several phones.
Yes, definitely use the Google contacts.