I recently bought Cities XL 2011 and have been a SimCity 4 player for years. Here's my input:
SimCity 4 Deluxe: This is the most powerful and in depth city building game ever made. The possibilities for creating your dream city in this game are much greater than in any other city game. However, there is a downside. You need to make use of the mods available for download at this site and others like it to get the most out of SimCity 4. If you don't, you will find yourself playing an outdated game without much variety. The possibility when you add in the mods is almost limitless. So why is this a downside? Well, there are so many mods out there, and many of them require many other downloads of textures and various other features to work. You can spend more time downloading these things than actually playing the game.
Cities XL 2011: This game is nice and easy to get into. Its the best City building game I have seen since SimCity 4. The graphics are beautiful, it has a fully 3D environment where you can zoom right down to street level too. You can place winding roads easily as you are not stuck with a grid system like in SimCity 4, where building winding roads is quite a challenge. The downsides to Cities XL are that it is demanding on your computer, and there is not as much variety as SimCity4 (if you take into account SC4 mods). Transport options are particularly limited and at the moment new buildings can not be added to this game by modders. Unless the company who make the game enable us to do that, it will never grow to replace Sim City 4 as the best city building game.
So to round up:
Simcity 4 Deluxe is the game to choose if you want to spend lots of time and effort making a beautiful city, and are willing to spend lots of time finding and downloading modifications. If you are essentially looking for a city building art package rather than a game, its the way to go. Its great, but believe me, its not easy and it is very time consuming.
Cities XL 2011 is the game to get if you want a great city builder that works on its own without having to spend hours upon hours searching for and downloading mods. Its easy to get into and learn, but not so simple its boring, its a good game. Maybe in the future if it gets the support it deserves from its developer and the modding community it will grow.
For your situation, reading that you want it for your family, I would suggest Cities XL 2011. SC4 would only be more suitable in the hands of a dedicated player with lots of time to spend.
