I’ll go with B on this one. Yes there are better paid VSTs out there but as far as I’m concerned, you’ve already paid for quite a lot of them by purchasing Cubase. I do have a few 3rd party plugs but if I was confined to Cubase, I would have no problem. They just have to be smartly used. Some plugs are only as good as their programmer.
Some instruments are pretty close to excellent. In my opinion, guitars and saxs are hard for any synth to emulate because they have so many nuances. For these you may have to upgrade to something that has more samples per note.
Drums, basses, keys, horns, strings and some sound fx pads are actually very good. FX plugs have carried me pretty far in my final mixes. If you need any final mix samples, let me know! (mind you, I’m only upgraded to Cubase Studio 5)