It depends on what you mean by best. For the average user a phone with a snapdragon 400 with 2 gb of ram should be enough. If however you are a power user a snapdragon 800 series should be enough with 2 gb of ram. The fastest CPU so far is the snapdragon 805 which is used in the GS5 LTE-A. I should also note that anything more than 2 gigs of ram is only needed if you take a lot of high resolution photos and videos
