I personally always go with Abit motherboards... I don't know anything about their Athlon line, but a long time ago me and my friend both bought the same Celeron 300A chip, but I bought an Abit BH6 and he bought the equivalent from Asus because Tom's benchmarks said the Asus was faster... well I just went with the little retail fan, and my friend ordered one of those iceman fans with 3 huge fans on it and a massive heatsink, and put it on with that heat conducting goo stuff... other than that, we got the same case, video card, etc.
We both over clocked our CPUs to 450(100), and my Celeron in my Abit was rock-solid stable from day one. I even ran it through a low-resolution Quake 2 looped timedemo (running at about 120 fps) for 6 hours straight with not the slightest problem. My friend's Celeron in his Asus with the big fans was never completely stable, and he ended up running it at 300 mhz, while I kept mine at 450.
Now I know not all CPUs are the same, and he may have screwed up his settings or something, but even if it's just for good luck, I'll always go with Abit motherboards.