Using InDesign and linking to external files via
File > Place is generally the best method.
While copy/pasting is certainly possible from Illustrator to InDesign, the paste can sometimes be problematic to edit later depending upon the actual artwork. Using the Place method allows you to edit the original, in Illustrator, then the link will update.
Placed vector images should look great if your display settings are set properly. Check
View > Display Performance. I think by default it may be set to
Typical. Try setting it to
High Quality. You should see instant improvement in the display of your placed Illustrator files.
The display performance setting is there to allow you to view low resolution proofs while working in an effort to speed up screen redrawing. This was pretty critical many years ago when it was introduced. With the way technology moves, today's systems, and video cards, are capable of more faster so often you can simply leave it on 'High Quality` and forget about it.
To set the
Display Performance setting default, with no document open in InDesign, choose the option you want from the
View menu. Or, again with no document open set the
Preferences > Display Performance to what you prefer.