Backup Exec is cool for small backup environment where tape management is not a problem. Also library support is not so cool in Backup Exec. Netbackup is the king when you have a big environment. It supports most of the available libraries and it does very well in managing the media. For example in Backup Exec you have to label your media Daily1, Daily2, Week1, Week2 etc. And then you have to make sure the correct media is in the library ie daily if you are doing daily backup.
In Netbackup, all these functions are performed by Nebackup and you don't have to worry about daily, weekly etc. You just have to make sure you have enough scratch media.
Let me know if I have enlighten you.