Without any experience with these kits, my guess is that the 381's will have higher top speed, while the 570's will have quicker acceleration, but only up to a slower speed.
Also, that first kit only has two 381oz motors, and one 960? That 960 is not going to work well for your other axis.
And if using belt reduction drives, you really want to use motors with 3/8" shafts.