i would like to buy a home theater projector how do i know which kind/brand has the best quality?

As a professional that sells projectors for a living you have lots of options to choose from.  I-DLA projectors offer a better picture overall. DLP Projectors offer great picture of a good price, and the LCD's offer a good picture for a great price.   For a great quality projector you should consider these three.  There is a price difference in each, but not a huge difference.  Look at the Sharp 1080P DLP theater projector which retails for about $2400, Panasonic LCD PTAU-4000 which retails for about $2100, or the JVC I-DLA theater projector DLA-HD550.  You can't go wrong with any of these.  The JVC is probably the best, followed by the Sharp DLP, the the Panasonic LCD.  When you are looking at known name brand projectors it hard to go wrong with any of them.  Stay with a name you know and you will find the right projector for your theater and wallet.