I've tried all three, Hotshots, Rev-X, and Archoil 9100 now.
Hotshots made the least improvement. It is found locally in a lot of places though so that is one benefit. It's not a bad product, just didn't work as well as the others.
Rev-X worked very well. It is expensive though at $70 for the two bottles needed for an oil change. Yes, I tried going to one bottle like suggested after the first "treatment" it didn't work as well as 2 bottles did. The bottles are 4oz each, so 8oz total for treatment.
Archoil 9100 worked a little better than rev-x and a lot better than HSS. It's also less than half the cost of Rev-X. Though, again, you need to order it online in most cases. I buy the 32oz jug for $65. That will cover two oil changes. It needs 16oz of treatment per oil change.