Hi Healthyeating,
Sorry this took so long but I thought someone would have answered this one quickly. Brewed tea generally makes a better tea than bags because tea bags contain bits of tea leaf rather than whole leaves, and small bits go stale almost immediately because of the amount of surface area exposed. You also need the hot water to circulate around the tea leaves and tea bags don't allow this to happen as well. Larger leaves are more flavourful and don't go stale as quickly.
There are some good quality tea bags out there but as a rule bags are a good way to improve yield by putting more of the rubbish in them. You know how it works the bottom line is always more important than quality, I hope no tea manufacturers read this or the screams will almost be human.
Cheers