We have both rats and piggies here. I've had rats for longer, as our 4 piggies have only been with us for a few months now.
The one thing I will caution you on, rats can be every bit expensive and probably more than pigs. Since my piggies are still new and received clean bills of health at the vet, I can only speculate they might not be as "delicate" as rats can be. But rats are definitely NOT cheap pets. I have spent thousands of dollars at our rattie vet, over the years.
I do think you can probably make more room for ratties, as you can build up. We have a 3'x20"x5' cage that is sized for 12 rats (we have 7 in it) that fits in an area smaller than the table we have our 2x5 piggie cage (with a ramp down to a 3x3 area below the table).
I find the piggies to be much more messy than the rats and require more frequent cleaning. Our rats are easier to litter box train. Although the variety of food is more with rats (they eat a lot of what we do), we definitely go through more food with the pigs. We are at the store buying veggies a couple times a week. And of course they go through a lot of hay too.
Although I adore my piggies and can't believe I waited so long to finally get them (I'm in my 40's), they just aren't as cuddly or people friendly as the rats. My piggies are rescues, so we really work with them. I love the sounds my piggies make too.
But if I am unable to take them out and hold them everyday, they seem totally ok with that. In a way, they are lower maintenance on the human interaction scale than the rats.
Rats require a minimum of "out of cage" time each day. It's fun to have them with you and to ride on your shoulder, but you also need to have a designated play area for them to roam, run, interact with you etc. Our play area is the headboard of our bed (we have one of the cabinet style head boards with dressers on either side, so it's an area about 7 feet long, by 14" wide) with access to an old built in cupboard we took the doors off of. We have the two large shelves lined with fleece and have igloos, hammocks, litter boxes, food and water. They run back and forth and also hang out on the bed with us while we watch tv in the evenings.
I will admit, rats are my absolute favorite pet. They know their names, come when called, adore me, love attention, are THE smartest pet (and I have a cat, dog and 2 bunnies too), and I can't imagine my life without them.
The biggest downfall of having rats as pets, is their short life span. Rats are definitely the heartbreak pet.