Well a interesting topic.....we have both of these cars in our driveway....as for which one is better....better is relative....is pure speed is what you are after then the MSP is " better ".
The MP3 feels much more " refined " vs the msp....the steering is euro spec ( slightly tighter ratio's ) and overall the car rides better smoother, softer and much less jerky than the msp.
The mp3 did not come with ABS which was kinda a bummer, both cars " feature " the infamous clunk and scruntch in the front end.
If you want a overall nice balanced car and top speed is not super important, the mp3 is nice balanced, well equipped, sporty car that handles well.....my vote would be the MP3. The MP3 is much rarer these days as well and with the addition of a CAI it is by no means a slouch.