which is advisable ... to download 500MB or to download 4GB in ubuntu ,GEU , mandriva ????? will be any performance difference and usage between ubuntu 500MB or 4GB ??
You mean how many distros? There are literally thousands available. You can even remaster a unique distro compilation for yourself. Since you're a beginner, stick with the usual suspects like the *buntu family (choose one depending on your requirements and system config).