Pepsi is one of the worst drinks in the market today, both through its horrible nutritional value and their lackluster taste (and aftertaste).
Compared to its foremost competitor Coca-cola, Pepsi is just way too sweet, leaving a filmy feeling in your mouth and a bitter aftertaste. While this is a more prevalent problems in most sodas in general, it is especially more so for Pepsi. I made the mistake of drinking Pepsi when I was really thirsty (water was not available). It did absolutely nothing but make me more thirstier. The diet brand is bitter as well. You call this refreshing? No way.
Sodas like these have their zing through their carbonation. In which case, better drink it quick, since Pepsis carbonations goes 60-0 within five minutes, leaving you with merely a puddle of black water...enjoy. The fact that their carbonation goes by too fast is especially frustrating when it comes to their 2-liter variety.
I thought I can turn to Pepsi subsidiaries for some help. Mtn. Dew is good for a while, but then the taste gets old too fast. 7-up is crisp, but a bit too bitter.
Finally, on the subject apart from the product itself--marketing (which reflects on the company in general), Pepsi strives to gain their share of the market through manipulative taste-testing challenges (I picked Coke by the way), pointless commercials that often pokes fun at their competitors and often filled with glamorous music.
The average Pepsi commercial has enough substance to fill a hot-air balloon. People who choose their soda based on Michael Jackson or Britney Spears choice have big problems--but just the kind of captive audience that Pepsi is after. Furthermore, for as much time they spend deriding Coke, they have not made much improvements. Coke has not responded with attack commercials on their own. Except for a few, most Coca Cola commercials are more wholesome.
Taste, Marketing and style is what really makes Coke the better product than Pepsi. Does it matter? Probably not in the big scheme of things. In the end, people will grab what is on sale on the shelf of Safeway-- whether its Coke, Pepsi, or Dr. Pepper-- no matter what Britney Spears is drinking or (supposedly) singing.