Okay let me put in my two pence, since Vice City is my favorite GTA.
Setting and Location : Vice City just looked amazing for it's time. It was a near-perfect re-creation of 1980s Miami, it captured the city's glamorous, sunny, tropical and Hispanic vibe and feel so brilliantly. GTA V's own graphical rendition of Los Santos looks just stunning, even more so at night, the city really does feel like LA. The weather effects are surreal, I just love the sunset and sunrise. LS could have been bigger, but overall Rockstar did a great job. Draw
Game Length : Vice City's main story took me a good few months to finish and complete, and in addition to this, there were so many different side missions and activities in the form of asset-building, freelance, odd jobs etc - so I found myself playing the game for a very long time the first around. GTA V in contrast, had a very short main story and the side missions, although similar to VC,were very few and far between. I finished V in less than a month, and not much was left to do, and I have not played it since. Vice City wins.
Gameplay : Both Vice City and GTA V contain many examples of classical, high-octane, and explosively fun GTA action within elements of their gameplay. But Vice City had a better structure and style to it's gameplay - it's rags-to-riches theme offered such a rich variety of fun and interesting gameplay elements both in and out of the storyline. In VC you played the roles of a drug-dealer, a hitman, mob boss, an extortionist, a businessman, a wealthy tycoon, a real estate mogul and back to being a straight-up violent and murderous thug. The city of VC itself was just great to explore in free roam, random gang war shootouts erupted in the streets, there were SO many accessible interiors for it's size. GTA V had some brilliant gameplay moments in the main story indeed, especially with the heists. But V's missions were very limited in it's variety from the second half of the game onward, especially outside of the story missions in V, and the small amount of individual side missions of the protagonists were not that interesting or anything special. Also, asset-building in V is just not as fun as it is in VC, the asset side missions take too long to be available to the player. Once again like GTA IV, V had no random shoot-outs between gangs in the streets, the element of danger was missing from the hood. Vice City wins
Main Storyline: Vice City's story had all the classic ingredients to make a great GTA story. Big drug deal gone wrong, working for Hispanic drug cartels, street gang wars between the Cubans and Haitians, taking over the city's rackets and building an empire, internal Mafia feud, betrayed by your closest crime associate, I could go on. VC's story just made you never to want to put the controller down. GTA V in contrast had some great moments in the story in very patchy form - Madrazo's periodic involvement, and conflict with Michael, the Balla/Families gang stuff early on, Trevor's beef with the Lost MC and redneck gangs - all that was very good. However most of V's storyline was swamped by that boring and uninteresting corrupt FIB agent/cop stuff. Sometimes, the plot felt like something out of Splinter Cell or COD, which really put me off that part of the story. The Merryweather stuff was kinda far-fetched too. So in short V was mostly about heists and being a lapdog for bad cops and government agents. This was not classic GTA material for a GTA story. Vice City wins.....by a large margin too
Protagonists, Antagonists : Vice City produced the most all-round, pound-for-pound best GTA protagonist in the entire series - Tommy Vercetti. Tommy was everything I could want in a GTA protagonist. A prison-hardened, Mafioso with a cold, murderous instinct, totally unforgiving and fearless, but yet ambitious, highly driven and motivated, and very loyal. GTA V had Michael the charismatic, but dull middle-aged guy (and a self-centered snitch), Franklin was straight gangsta, but he whined and moaned a lot and Trevor was just annoyingly crazy and wild, plus dirty and despicable. VC had much better antagonists in Ricardo Diaz and Sonny Forelli - one a paranoid, homicidal drug baron and another a ruthless and greedy Mafia boss. I'd rather have them over some stupid polo-shirt wearing corrupt top cop and a corny rich guy that sounds like a news anchorman. Vice City wins.
Overall Vice City WINS