Fast answer: Having a few high level skills is better than having a lot of low level ones.
Long answer: Depends on your build.
You’ll have to take in consideration synergy between skills and classes.
Why do you think Wiz3 goes well with Ele3 ? Because Ele has some very long cast skills and Quickcast(from Wiz3) reduces casting speed by half.
Why most people that go Rodelero at rank 4 went Peltasta at rank 2 ? Because Pelta skills already uses weapon and shield, that doesn’t interfere with Rodelero theme.
Second case are classes that have really good benefits at C1, but don’t have a really good improvement at later ranks. For example, people like to go Scout C1+Musketeer to PVP, because Cloaking go well with Snipe to oneshot people at arena. For that reason you don’t need anymore than one rank in Scout.
And third case are classes that have good skills at C1-C2, but don’t have good improvements at C3. Like for example Archer C2 have Swift Step Critical buff which is pretty good and it’s uptime is already 100%, you don’t need to go Archer C3 to get the most of it.
When choosing a class on class quest change you allways have to take in consideration that you’re gaining something by going class X, but you’re also losing something for not going class Z. Evaluate what’s more important for your build and go on. Allways plan way ahead of what you are now. Make a build before you start and go for it.