It is not important which quad-line kite you purchase; they are all difficult to fly for anyone who is just beginning. Some kites, because of their design, are very difficult to control, even for experienced fliers. Talk to the people on the German forum and buy something that is easy to learn. Stay away from small-sized and fast-speed kites, as these will give you very little time to react. For the same reason, use lines that are 30m or longer. Larger kites and longer lines are more forgiving to beginners. Finally, buy what you can afford, but remember that it is favorable to get a good quality used kite than a poor quality new kite.
Most of all, keep smiling, have fun and don't forget to breathe.