If you are a beginner then u must know that Desktop applications are installed on personal computers whereas Web applications can be accessed through internet. Now both have different advantages and both are good in their own way. As in Desktop applications can only be installed on personal computers so they are trustworthy u can use it as long as u have ur comp within reach whereas Web applications are accessible everywhere because it is accessed by internet.
I have found music software to be a great boon for composition. I think it has set me forward many years in my composing abilities. I used Guitar Pro. I've also tried free music notation software and most of these aren't very good: they are buggy and not very intuitive.