There are many opinions on this subject. A lot of things can be used to clean the track, train wheels and pick-up rollers. Using non-polar solvents increases the time between cleanings as they help reduce arcing which leads to carbon build-up on the track, pick-ups, and wheels. Carbon build-up increases electrical resistance between the train and track causing increased arcing, causing more carbon build-up requiring more frequent cleaning.
I used to use alcohol, but after reading the recommendations of others here on the forum who clearly understand electricity and chemistry better than I do, I've switched.
Mineral Spirits is one such non-polar solvent which works very well and doesn't leave a slippery residue behind. I find it removes carbon deposits from the track with less effort than 91% isopropyl alcohol.