Note that the GeForce4MX 420 has only a 128-bit SDR memory bus (similar to the original GeForce2 MX and MX400). This will underperform the 128-bit DDR memory on the GeForce4MX 440 and GeForce4MX 460.
I haven't seen a head-to-head benchmarks, but for PCI you might still be best off with the Radeon 7000 DDR.
With either the Radeon 7000, GeForce4MX or GeForce2 MX, you are looking at DirectX 7 hardware T&L. You will not get the programmable shaders in the DirectX 8 boards like the GeForce 3, Radeon 8500, or GeForce4Ti.