FP and RP are two totally different beasts. FP demands a completely dark, dedicated room for the most part. If you can do it, the size of image thrown will blow away any RP set available (note: talking consumer RP type sets, not rear throw projection systems).
Look at your environment and watching habits first, then make sure you've seen both in action. Then you'll know the answer to your question.
Look at your environment and watching habits first, then make sure you've seen both in action. Then you'll know the answer to your question.