Pepsi Throwback with lemon.
Pepsi floats are better, too.
Coke is fine on occasion (especially when mixed with orange Fanta), but I'm pro-cane sugar and Mexicoke is expensive.
Throwback is becoming increasingly hard to find, so in my search for a new soda I've found that the Whole Foods brand is surprisingly delicious. It tastes fresh, pure, and not overly sweet....and, er, it's possibly tastier than Coke. *gasp*
I've quit on soda, though, so it's a very rare treat unless I get my hands on Italian soda. :P
Pepsi still reins taco supreme.