100% Guinea-Pigs but I've never kept rabbits or rats .
The appeal of rats I can see - they are clever,agile , (unlike guinea-pigs who are not the sharpest tools in the shed and like to be on terra firma)
A rat residence can be many levels so you can go up in a small footprint . Guineas take up a huge amount of floor space .
I'll give you the downside of guinea-pigs :
They are messy . They don;t do toilet training though our boars did make a little pile of droppings where they slept , it was more laziness than tidyness.
The hay gets everywhere . The hay smells , guinea-pigs don't provided you keep them clean. The hay and the fur can be very allergenic but guinea-pigs need unlimited hay (they eat pretty constantly) and do insist on Real Fur which is a poor show for a vegetarian 
They are prey animals and very vunerable . It makes them sweet and endearing because they don't kick or lunge at you . They cannot run as fast as other small animals and cannot turn their heads quickly .
They can bite . Don't believe people who say they never bite . They're rodents with teeth . But I would say 99.9% of biting is fear, pain, your hands smelling of food or mishandling . They have no defences , it is amazing that they don't bite more . One of my sows "gnawed" not a bite but a toothy kiss .
They need protected from everything : heat , cold, damp, draughts, predators, poisonous plants .
They cannot be sick. What goes in has to go through them.
They are complex healthwise . And as prey animals get ill very quickly and hide it . You will need to know them well to pick up the early signs. And get a Cavy Savvy Vet - they are Exotics .
They need company of their own kind, if you have boars they're best in a pair . Lots of room.
They die
and leave a huge space in your heart so you end up in a never ending cycle .
They are a bit (covers any guinea-pigs ears) a bit limited . Some will say boring !
But the upside is they are beautiful, gentle, chatty , greedy , very bribeable little mammals .
No matter how much your DC say they'll look after them it'll be You as the Adult who will do it . At the end of the day the buck stops with the responsible adult .
My DD and I shared our pigs so shared the cleaning, feeding, cuddling , bathing, claw cutting . It is hard work !
Some days if she was away , or ill or busy with homework it was "Mum can you do the pigs"?
But the next day she did it .
And if we were away or ill, DH did it .
We have cats now after the last old piggie died . I have to say they're easier as they're independant . They have their own feline requirements and shred the carpet and wallpaper , but we love the little monsters !