Unfortunately, as you have probably found out, the motherboards for the AMD and Intel processors are not compatible - so once you make your choice, you're committed to the processor manufacturer until next mobo upgrade (assuming the chip manufacturers stay with their current socket long enough to be able to upgrade without another mobo change!!)
"Nobody ever got fired for buying IBM" - and the same applies to Intel. However, the Athlon option does have some interesting plusses. The most significant (IMO) is the processor-to-bus ("front side bus") speed. With Intel it is currently 100MHz (or 120?) but the Athlon can drag in data and ops from the memory at 200MHz - if you buy a mobo that has this capability and make sure the memory is compatible. Talk is that AMD will eventually get 400MHz processor-to-bus but I don't know if current mobos will allow you to upgrade to this.
You should also consider that most of the mag tests show the Athlon performing some 10-15% faster than an Intel of the same clock speed - and your choices have AMD with a slightly higher clock as well! (this performance difference could well be due to the front side bus speeds)
My own caveat is the hard disc speed - while our processor speeds have been ramping up over the last several years, we have not seen quite such an improvement in disc access speeds, so I tend to think that the HDD subsystem needs careful study. You can help this with GOBS of RAM (the best Windows upgrade ever invented!) but even with stacks of RAM caching the HDD, you still have to get it of the drive at least once every time the computer is switched on. So if you're upgrading an existing system, remember to consider if you are going to have to allocate more hard earned shekels to a new hard drive in the near future, in order to get the best out of your 700/750MHz procesor!
Good luck - and have fun!