1

Personally I would skip Guadalajara for all sorts of reasons - you can easily drive to PV in one day from Guanajuato.

2

Guanajuato deserves more than 2 days & Guadalajara more than 1. I'd do at least 3 & 2 the 2 places & my choice would be a week in each.

3

I would stick to daytime driving, especially if you are not on the toll roads. You've got to stay alert for speed bumps ("topes") and you can see them much better in daylight. If you haven't been to Tequila, this would be a good opportunity. Also, there is a small archaeological site (Los Toriles) that you will pass by as you approach Ixtlan del Rio via the "libre" (non-toll road).

You will see a lot of black volcanic rock near Ixtlan and, of course, fields of agave. There is a (toll) road that will allow a short-cut to bypass Tepic. It will take you to Compostela. You'll reach the coast at Las Varas. There are steep hills, tight curves, and few guardrails.

You could also take a more southerly route I think, through Ameca and Mascota, but I've never been that way and can't say anything about it.

4

we did this last year because it was more convenient & cheaper for our family of four
PV to Aticama then to Queretero, SMA, Guanajuato and back to Guadalajara Airport ( drop off fee ) for return flights home
we tend to enjoy daylight hours so much walking and talking the sites we drive way too much in the dark but those toll roads are as good as you're going to find anywhere and frankly there are very few cars on them - some big trucks but always open lanes and you can fly
like anywhere give a good look at your vehicle, establish pricing, buy insurance and have a great trip

and if you are lucky you will park near where we did and exit the tunnels to the finest taco stand in the world

5

oh and now I have re read your question / whole new element to the equation

rental car Leon to PV / so not returning car to where you rented it and encumbering a drop off fee

establish that fee now as it will impact your calculus on mode of travel
we dealt w/ that on our trip and I'd hazard guess of fee of about $ 223 US dollars for that drop off

6

Thanks all for the feedback! Much appreciated. I think were going to bus it from Guanajuato to Guadalajara and then either rent a car or bus it to PV.

7

ETN has terrific buses/connections Guanajuato to Guadalajara. Mine last week actually took less than 4 hours including a short stop in Leon.