It's too broad of a subjec to be discussed here.. There are lots of factors you should look into and below are some -
How much money you have?
What problem are you trying to address?
Size of your Full/incremental Backups
Data Retention.
Data type
Some VTL provides compression only and some provide de-duplication. One with De-duplication may be little expensive than one providing compression. Some has built-in compression/de-duplication engine to stroage like Data Domain and some have additional appliance like Diligent and you can use any storage underneath it. Some provides you capability of exporting data to tapes without going through media server without an update to NBU catalog, whereas some vendor like NetApp has special hooks to NBU catalog and it let you create the tape and update catalog too. With NBU 6.5 this has been enhanced further.
NetBackup Pure Disk provides you something similar to a VTL solution and currently is available for remote offices (over the WAN backups). With 6.5 release it will be available for Enterprise also.
In Nutshell, recommendation from person A may be not good for your environment if your environment/requirement are very different. You will have to do bit of homework to list your requirements and then see who fulfills your requirement without adding overhead to your day to day work and with least management work.