bang for your buck is a tough question as depends on your individual reaction to brand and dose. When dieting for a show, 2 iu is perfect (for me at least) as just speeds up process of shedding bf. Currently using 3iu a day (IP Yellows) split into am and pm and has done a nice job of keeping me fairly lean while eating a bit less clean during the summer.
pick a brand from a sponser, try 2 iu and see how you feel. If at 2 iu you get some thingling in fingers then u know it's affecting u in a positive way. Go to 3iu and see how that feels. For me w the Yellows, at 4 iu the pain in my hands is terrible in the middle of the night so I stick w 3.