I generally prefer to avoid using abbreviations, as long as it’s not too awkward or difficult to use the longer form. It’s just a case of style really. I understand the need for abbreviation in language, but sometimes abbreviations can just seem too lazy, too short.
Which is why I’ve been trying to use the word application lately, rather than app. It’s just not working out though. First of all, no-one else is using it, and app just seems to be more appropriate. Mobile phones are so small, and apps can seem so ephemeral (especially to me, because they don’t have any real physical existence, which is something I’ll never quite be able to get my head around), that the short and simple app just seems right. At least application still has its own exciting life of job and college applications to enjoy!