Good question. Well, I cannot truly say which option is worse, but I do have solutions for either room.
For the room next to the garage
Is it possible to insulate and seal the wall from the garage side so that minimal or zero fumes are transmitted into the house? We generally do this to the homes we work with.
First we seal all the little hole or cracks (including electrical outlets, ducts, and faming spaces, etc,) that may be places where air is transferring. This has to be done fairly meticulously. An energy rating company may be a good person to call to do this as they are super aware of where a house loses energy in the form of hot or cool air passing through walls.
After you have sealed up the leakages, insulate the wall with foam or dense pack cellulose or similar insulation that will further reduce the occurrence of cracks where air can leak but also create a thermal barrier that will stop the air from moving through the wall in the first place. Be especially careful of any ductwork that may cross between garage and house (Some people have their HVAC equipment in the garage.)
For the room next to the electronics
Here you may want to first do some EMF testing. It is always surprising what is and isn't giving off the most EMFs.
For example in the last new house we built there was a lot of WiFi. The clients very were concerned about EMF. When we tested, the WiFi was actually the least culprit. Things like the Microwave and TV were the worst, as was the main electrical 'trunk' running up through the house.
In this case we ended up wrapping the electrical trunk wall in sheet metal (beneath the sheet rock.) The clients opted to not have a microwave after learning about the EMFs and they kept the TV in one remote room. I realize this is not an option for everybody!
After testing and seeing where the bad spots are, maybe you would consider taking down the drywall on one wall of the baby's room and installing a layer of sheet metal, and re-installing drywall.
After reading these solutions, maybe it is easier to decide which option would be better for you? I hope so and best of luck!