Here's the facts
http://www.cabo-fishing.net/weather.htm
Average January high 74 not bad but the low is in the low 50's. Heck I get that at home. Plus the Record low is 36 F for January & 31 for February. With no heat source that's COLD!
In Contrast Zihuatanejo is in high 80's/low 90s with lows in the mid 70's.

Guess I'm just lucky. Because it was HOT.

For Comparision PV is on average 6 degrees higher.
http://www.puertovallartatours.net/weather.htm

I believe you, you don't have to convince me! The further south you go the warmer it likely will be (well at least until you're the other side of the equator). That's true.

And here's Zihuatanejo a full 14 degrees warmer on average.
http://weather.msn.com/monthly_avera...ns=wc:MXGR0136

Suze I posted these for the OP. I know you are a experience Mexican traveler & expert. If I had a question about PV I did not know the answer for you would be my first source.

Again, thanks. I still haven't decided.

Suze, I know what you're saying about getting away from the Marina and Playa Medano in Cabo San Lucas. Someone made the comment above about "more traditional Mexico." Cabo San Lucas can't compare to San Jose del Cabo in that regard. That's what I was addressing.

I have ONLY been to Los Cabos in August or September. I was last there this past September. (It was work-related, in fact working on the next edition of the Fodor's guide.) The place is a furnace that time of year. I have to start going other seasons of the year. I'd love to experience it in January. :)

Thanks again everyone. I wound up booking PV for January, staying at La Jolla de Mismoloya. It seemed like a good deal.

Thanks Jeff~ I'll have to get off my lazy... lounge chair next trip and get over to San Jose del Cabo and check it out! It's just I was truly surprised by how 'mexican' the downtown area was away from the main tourist drag of Marina/Medano. I'm used to PV where things are more mixed together.

andrews~ That's a good choice. Do know that Mismaloya is a ways to the south of downtown, so you'll need to use bus or taxi to get around outside your hotel/resort area.

Nice choice. Just ashort bus ride from Old Town.

I'll have to watch Night of the Iguana before I head down there.

PV is only 2º further south of Cabo.
Los Angeles is 3º further south than San Francisco.