Sugar is sucrose (C12-H22-O11, sweetener)
Equal is aspartame (C14-H18-N2-O5, sweetener), dextose and maltodextrin (fillers)
Sweet-n-Low is saccharin (C7-H5-N-O3-S, sweetener) and dextrose (filler)
Splenda is sucralose (C12-H19-Cl3-O8, sweetener)
(H = Hydrogen, C = Carbon, N = Nitrogen, O = Oxygen, S = Sulfer, Cl = Chlorine)
I started as a kid eating and drinking products high in sugar and corn syrup, both built with glucose and fructose molicules.
I never liked the taste of aspartame, so I never drank it.
Eventuall, I found several drinks made with aspartame that I didn't find revolting (Diet 7-Up, ICE, Safeway carbonated fruit drinks), so I began to drink them. Eventually, sugar became "too sweet" for me, so I stopped consuming lots of products with it... namely soda.
Recently, I made the switch over to sucralose by way of diet Arizona Ice Tea. Carbonated ICE and Diet Rite also switched over, so I drink those too. Having consumed both for nearly half a year, aspartame is now starting to taste odd for me. Regular diet coke tastes bad now. Coke Zero has different ratios of potassium benzoate to aspartame than regular Diet Coke, so it doesn't taste as bad. Unfortinately, Coke with Splenda tastes like flat Coke Classic, so I tend to avoid it still.
So in short, if you're used to Spenda, it tastes the best. If you're used to Equal, it tastes best. If you used to sugar or corn syrup, all three diet sweeteners taste like crap. If you drink diet sweeteners, glucose + fructose based sweeteners are too sweet.
No major soft drink company uses Naturlose (commercial name for D-tagatose, C6H12O6 enantiomer) yet. Its a low calorie sweetener that has only 10-15% of the calorie value of sugar. It is supposedly as close to the real thing without being it.