The Impala has some good power (1-V6, 2-V8), their biggest engine is a 300hp V8. The Charger has bigger variety (1-V6, 3-V8) with 2 HEMIs, a 335hp 5.7L and a 400+hp 6.1L.The Charger is a great "bang-for-the-buck" starting at $19,000 for a 235hp V6 SXT, the Impala is worth $5,000 more for a base 230hp V6 model. The Charger looks much more aggressive than Impala, but the Impala is more luxurious.
If looks and performance at a reasonable price is what you want, go for a Charger, for a more comfortable, luxurious car, go for the Impala. I like both models, yet choose the one that's best for what you want in your car