Which of these bios (X-2 4981.67 ...M-7 ...M-8) is the better one and why? And how many times can flash the bios. My chip is Xecuter 2.3B Lite.

Thanks

Depends on opinion, choose the one that has the features you like.

You can flash as many times as you want provided it flashes correctly (not incorrectly installed, etc.) Also use a bios that works with your xbox or else you will find it hard to reflash the bios, both M8 and 4981 will work with 1.0-1.5 but i believe only M8 and x3 bios's work on 1.6's (may be wrong, but thats what i've heard).