The El Mirador is a very nice park in San Carlos. A little too cool for us for the winter, but we always stop for a few weeks on our way North in the Spring. It is clean and the staff are very nice. Also, a wonderful restaurant, pool and hot tub. It is usually very windy.
we stayed there on our way back from Mexico in April & it is a very nice park. Probably one of the best in Mexico. 30 amp power, good water pressure, lovely views & sunsets, pool, paved roads with solid gravel pads, WiFi ( although it depends where you are parked). It is a little way from the main strip if you don't have a car, we bicycled.
On the way down we stayed at Totonaka, which is good although not as advanced, but near the beach & all the shops & restaurants. Also has WiFi.
We spent 4 months in Mexico & travelled 6000 miles....loved it. Don't believe all the horror stories. People are lovely, diesel is cheap, campsites are reasonable, but don't expect the same standard as north of the border. 30 amps is the best you will get & the voltage is not regulated, so it can vary from under 100V to over 130V. We had a voltage regulator & surge protector fitted & it would regularly cut off the power. Normally you will get about 15/20 amps, which is enough to charge your batteries, but not much else. Water pressure is usually very low & sometimes non-existent. it's usually better to fill your tanks & run off the pump. A lot of people put some Clorox in the fresh tanks. Filtered water is readily available for drinking. It's all part of the adventure.
Everybody we met has the Church's book, Rv'ing in Mexico, which is well worth buying.
There are lovely beaches, amazing ancient ruins, the colonial cities are well worth visiting, & there is also the Copper Canyon which is bigger than the Grand canyon.