Choosing a tripod really comes down to what you plan on doing with it. The Gitzo 3 series is probably the best general use tripod on the market. Determining use will help you decided which model is best.
The XLS version is best suited for those that are tall over 186cm, (6’1”) often shoot from uneven terrain, occasionally need a higher point of view or shoot overhead a lot like birds in flight. It has a longer folded length so makes it more difficult to carry around or pack for travel. If you find yourself in any of the categories above it may be worth considering.