I should probably leave the Internet for having an opinion, but while I will be playing GTA V more, Rockstar put more effort into GTA IV. What makes me say that? For one, they only care about online now, ignoring single player gamers such as myself. They also completely ruined what a city feeling is. If I walk the streets, pedestrians call the police on me for no reason, honk the horn for half a second? They call them for that, GTA IV's AI actually worked, they helped you out, they weren't afraid of you, and at least I could let Niko walk the streets without getting in trouble.
GTA V has so many aspects lazily done to the point where I feel like they just gave up on this game, there's next to no building interiors, nothing to interact with, and the wanted system is a joke. I automatically got a wanted level for bumping a pedestrian, is that really how a city works? When it comes to playing, you have to make up what you want to do, sure I can come up with days worth of things to do, but having to rely on players making their own gameplay isn't a wise choice, at least in GTA IV I could go places, get some food, walk the streets, go do more activities, a whole lot of stuff that GTA V lacks because Rockstar went lazy, the map is beyond amazing, but putting 5 years of development into a map doesn't automatically make a good game. The vehicle handling is horrible, I love GTA IV's driving, but apparently to others it was terrible, so now we have this horrible arcade handling that ruins the driving aspect.
I may be biased, as I played GTA IV on PC (I played it on this horrible console I have before I got it on PC), where I used a trainer and modded it heaps, the trainer added more depth to the game though, being able to sit down in the park and take in the city, it was nice, if I try to take a walk in GTA V the pedestrians either yell at me or call the police. I will be modding GTA V a lot, and using a trainer (a never wanted setting would make the game more realistic). It will make this game better.
Rockstar had so much potential with this game, but they were over-ambitious and blew it, they threw us some lazily half-done game that looks nice but has features so badly done you can't help but be disappointed. The train is on a static route and doesn't do anything else, the city has very little things to do, the AI is the worst I've seen, etc... So many great features from GTA IV were thrown out for no reason whatsoever. If you have a feature that is good enough to work in an open-world game, why not re-use it? They re-used a bunch of things from GTA IV, nothing wrong with that, but some re-used things were done even worse. They put all this time into an aspect that they just disregard in the next instalment. Things like bowling, phone customisation, vendors, working AI, GPS voice, leaving the engine on, QUB3D, food outlets, I could go on with things GTA IV has that V doesn't. Imagine combining all the small GTA IV aspects with GTA V, you would actually get a city that feels like a city.
It may be a long post, but while I do love GTA V, as it's really an amazing game, there's no way it can be regarded as automatically being better. Niko is probably laughing at the LS life. I can see why many prefer GTA IV over GTA V, GTA V just feels... lazy. Not saying I could do better, but for a company like Rockstar, who are professionals in this, and who said this game would be amazing, it's not what I would expect...