Although VivaAerobus and Volaris are ULCCs, they don't differ much in overall experience as domestic AeroMexico flights. You're more likely to fly an A320-A321 on the ULCCs, with AM being 737s and E190s.
As mentioned by "jjbiv" be mindful of your luggage and personal items' sizes and weights and purchase your baggage accordingly.
Personally I prefer Volaris and Viva for domestic Mexico flights. Plus if you have any access to priority pass lounges, I also favorably lean more towards Terminal 1 at MEX than T2.
Safe travles - Enjoy Chiapas
I am leaning towards Viva because of the one experience i had. I need to check my bag weight and size (100liter) but I was planning on doing the better of the add ons just incase.