AMD AthlonXP Thouroughbred 2500+ (1.8ghz) is equal speed to the Pentium4 2.52ghz
AMD AthlonXP Barton 2500+ (1.85ghz) is equal speed to the Pentium4 2.52ghz HT
AMD Athlon64 2800+ (1.6ghz) is faster than all of them
The Althon64 3200+ (2.0ghz) was recently released and that processor now sets the standard for the fatest on the market, even surpassing the Athlon64 FX-51.
if you want to go price for price though, you can pickup an AthlonXP 3200+ for less than you can get a Pentium4 2.52Ghz Standard
and that processor is capable of keeping up with the P4 3.0ghz HT.
Upto you what you choose though, think about it's all down to which you prefer; as they both are on the same power length.
P4-M 1.3Ghz | 512mb DDR PC1800 | GeForce FX 5600 Go! 53.03 | DirectX9.0b SDK | C-Media 8738/C3DX | Windows XP 2004