good question!
well beta alanine competes with taurine entering the cell, also beta alanine causues flushing, something that we really dont need pre workout...also beta alanine needs to be dosed multiple time to keep concentrations high, it also needs to have an enzyme present to synthasize it... i used to take beta alanine a lot! and it worked o.k., but compared to carnosine it is way under par...
carnosine has a large number of benifits, it is a potent anti oxidant! a lot of people think that carnosine get ruined in the stomach, but this i have found to be untrue... i usually take 2-4 grams pre workout and another 2 or so grams during or right after to help with recovery... it really is one of my favorite supps, it is expensive compared to beta alanine but well worth the cost! carnosine is one of the supps you can feel a difference the first time you take it, i experience vascularity, and a "pump" or fullness of the muslces befor i even get started training.... taking it befor a leg workout is my fav. it really decreases lactic acid build up and make me recover a lot faster!
the taurine is good stuff as well, i take it post workout and right befor bed, it really helps me to calm my nerves... there is plenty of info about it out there do a search and see what you find.... you probably didnt notice much becasue you werent taking enuf of it, i buy it by the kilo....