2003 Buick Regal and 2006 Impala, which to choose?

I am looking for a used car and found the following two cars:
car one, private owner, 2003 Buick Regal LS, 57k miles, lether, sunroof, ABS, traction control, looks and dives ok, does not feel so powerful with the 3.8 L V6 engine, KBB private party price 6500, can get it at $6200.

Car two, from dealer, 2006 impala, LT, V6, 47k, looks very clean, just traded in yesterday, I have not test drive it. KBB private party price 9205, can get it $9300.

I will have long trip (1500 miles) driving. Which one should I choose?