For me, Pat's wins hands down. It's less a matter of the individual ingredients than the overall construction. Here's how they order their ingredients when they build their steaks.
- Meat (greasier; to some, a negative, but for me a plus)
- Cheese Whiz (slapped on top)
(all ingredients taste fresher and seem to be of a higher quality)
- Cheese Whiz (thinly spread)
- Onions (coarser chopped, spicier, and less cooked)
Now Pat's is superior because since the meat is in contact with the bread, the juices get to seep into the bread and meld with it (the greasier beef helps). Also, the heat from the meat tends to rise, thus further melting the cheese on top and creating a deliciously messy slurry of cheese, onions, grease, and juicy bread.
Geno's, on the other hand, spreads their cheese on the bread first, and then slaps the meat on top. The thin layer of cheese acts as an insulating layer, so the juice from the meat can't penetrate into the bread. Also, the cheese doesn't melt any further all that much, as the heat is radiating mostly upwards and away from the insulating cheese. Then you've got your too spicy onions on top all alone (you've really got to cut the spiciness by mixing with cheese for optimum flavor). Sometimes the onions get put under the meat, but this depends on the preparer, and doesn't help much since there's not enough melted cheese to produce a slurry. This adds up to a steak where instead of all the flavor elements fusing together into a hot and greasy mess, the steak is more sterile with each flavor element being neatly separated from the others, and tends to be drier.
The bottom line is Pat's is the flavor champ due to its scientifically proven construction of melding all the flavors together. Geno's is just OK, but it's really popular for those who demand fresh quality ingredients, a clean decor, and a neater and easier to eat steak.
Oh, and ya gotta get a bunch of the free cherry peppers to go with your steak!! Mmmm...