Now that I think about it, there's no real reason why the 360 version will have better legs, except for DLC, but there are a lot of good reasons why the PS3 version will have better legs (brand loyalty, attach rate, better sales, more strength in Europe).

I think the PS3 will have better legs, mainly because the ps3 is selling more, and most people getting the console will get GTA with it, because it is such a popular title. GTA is played by everyone, so when the casual gamers begin to come to PS3 (maybe more with LBP and price cut?) GTA should be boosted. However, I think that the DLC (if it is as big as everyone says) should boost the 360 version somewhat, but I still thing in the long term the PS3 will win out

yeah the ps3 version because the bulk of 360 owners got it on release day.

ps3, for all the reasons everybody already stated.

Ahh, but let me show you an example. Something I was actually thinking of writing about:

There are 2 different types of casuals!!!

As this week's American charts will show you, Grand Theft Auto IV actually boosted hardware sales, and this helped boost sales for games on both the platforms it was released on. While all games saw a boost, many of them were sports games, such as NBA 2K8, Madden, WWE Smackdown, etc. Of course, the Wii saw boosts for those sorts of games too, but that was mainly because it sold 400k units in America this week, an incredible amount. So, there are two types of casuals: Those that buy sports games, sandbox games, and shooters, and, of course, those that buy platformers, minigame titles, and other games that are for all ages.

Not only do we have a rift between the hardcore and casuals, but we have a rift in casual gamers themselves! I'm not sure LittleBigPlanet would appeal to the people who buy GTA4, but it's all very interesting to think about.

 True, but often you will get a boyfriend/gf situation, where one wants LBP, Singstar and the other wants GTA, Madden etc, so it could go both ways. However, it is the creativity in LBP that will attract people, though some may be put off by the rag doll facade, before looking deeper into the amount of creation avaliable.

also, Uncharted received a decent boost showing that it was not just casuals getting GTA now, many will be waiting for that price cut

I think initially XBOX 360 will show better legs but in June with the release of MGS or even the start of advertisement of MGS we should see PS3 version showing better legs for GTA IV than XBOX 360... as we just saw that with the release of GTA IV all games showed some noticeable boost... so i think PS3 is lucky that its going to have another major hard core game in June...

Just my theory..

There is no reason DLC will sell more systems/copies. The DLC is now targeting owners of the game. The DLC was the 360's selling point. The game sold to people who already had the systems. Now it comes down to new console owners and what they pick up with their purchase... Ps3 is winning week in and week out. Also when it is released in Japan I can see the Ps3 version outselling the 360 version by 200k (Yes it is nothing in terms of the big picture but it is still a nice number.)

I think the 360 version will have better legs in the long run because there are more casuals who own 360s since it has a larger userbase and the casuals are less likely to pick one up the first week. The DLC will help the 360 and the PS3 GTAIV failure thing will hurt PS3.

Predictions for this week:

NA
360: 900K
PS3: 450K

Others
PS3: 400K
360: 300K

I think the 360 version will have better legs. Since the PS3 version sold at a higher attach rate it will reach market saturation more quickly. GTA 4 is a game that caters to the type of fanbase the 360 is always accused of having so I think it will see continued strong sales.

The PS3 version will continue to sell as well, but I envision a CoD4 situation where both sell but the 360 version sells more.