it's got to be Yorkshire, Lancashire or Captain Scott ( proceeds from which go to the upkeep of the explorers camp in the Antarctic, now a museum ) That's the best tea for me, though hard to find.
When it comes to tea bags I really don't see the point in going for a cheap brand as you are only saving a few pence per cup. A supermarket own brand may be 1p per bag, a Tetley/PG Tips 2-3p per bag or you can get something decent for 4-5p per bag.
Personally, I like a pure Assam which I find to be robust enough without being too strong and over-powering. The likes of Ceylon and Earl Grey are too delicate for me.
I know the purists will say that you should use loose leaf tea but I find that too much of a hassle when I just want a quick cuppa.