Which alpine amp is better for powering my 2 Alpine 12" Type S subs (2 ohm subs)?

I thought that using the Alpine MRP-M500 (500w) amp would be fine for powering both my 2 ohm subs, but should i get the Alpine MRP-M1000 (1000w)? If so, why should i get the 1000 watt one over the 500w one?