Well, if money is no object, more power is better. But subs are part of your audio "ecosystem" and this question can't be answered in a vacuum. What are you pairing the subs with? If they are just boosting the factory head unit and speakers, then 300 watts might be okay. There are also considerations regarding the way you connect them. One sub has only one way to connect it. But two subs can be connected either in serial or parallel (let me know if you need me to explain that). With serial connections your amp will run cool, but won't be as loud. Parallel connections will make the amp push more power and run hot. A high quality amp might handle that. Cheap amps can overheat if "over-driven."
No matter what you buy, you'll need to tune the sub output carefully so its output varies properly with the rest of the system. It would be no different that bolting a supercharger to your motor without considering fuel delivery, tranny, tires, etc. When in doubt, consult a local professional.
2012 GT/CS, 6-spd manual, MGW shifter, 3.55s, triple black, Steeda Ultra-lite springs plus adj. panhard and upper mounts, Borla S-Type cat back, Hankook 245/45/19 fronts and 275/40/19 rears on TSW Jarama Hypersilver 19x8F/19x9.5R rims, Redline hood struts