We really enjoyed Puerto Vallarta. The city is very international, English is widely spoken, and there is so much to do. The food is incredible, especially away from the Malecon (tourist-y boardwalk area). The people are friendly and the city feels very safe.
Not having much time to experience "Cabo", my impression is that it is a nice diversion, but not for anyone seeking to experience Mexico. The natural beauty of the desert, beach, and sea is amazing. The shops and restaurants surrounding the pier area (the only area we had to explore) might as well be in any mall in the US. Maybe there is a real Mexican side to the city, but we didn't have enough time to find it.