Does anybody know the best place to go for cheap flights?

I have always gone with Virgin or BA but since looking at this forum i have seen that some of you use Travel City Direct.

Is there much differance in price?

I am buying a place in April and plan to go to Florida about 4 times a year and wondered if there were any frequent flyer discounts or if there is a way that i can get cheap flights or possiblr upgrades to business or First.