Berryman B12 is another additive I have used to clean out neglected fuel systems. This stuff is about 1/3 the price of Seafoam and is quite aggressive so use it with caution. I usually change the fuel filter after running this through a tank of gas.
Marvel Mystery Oil is basically diesel fuel or kerosene. It is probably the most gentle of the three I am going to mention. Many like to add a couple ounces per tank of gas each time they fill up for maintenance purposes. It is also one of the cheaper additives and you can get it in larger sizes for a low cost per fluid volume.
Seafoam is by far the most expensive. I have had good luck with it on engines. Again, if you haven’t had the fuel filter changed, it might be a good idea afterwards. Yes, it does smoke when you suck it in through the intake. The rationale here is that you stall the engine with some in the cylinders and let it soak for 20 minutes or so. Then you fire the car up and drive it like is is stolen, fogging up the entire area with smoke in the process! I have also put it in the oil about 10 minutes before an oil change on engines that have been cared for. The oil seemed a lot darker with this so all I can figure is it removed deposits from the dark recesses of the engine. I have also noticed this after changing a car over to synthetic. The oil always get really dark quickly after the change.
I would say that Berryman B12 is the most aggressive, Seafoam is in the middle, and Marvel Mystery Oil is the least aggressive. MMO has been suggested for sludge monster engines as it is a more gentle cleaner and won’t break loose all the crud at once, plugging your oil filter. If you add any of these to the oil, make sure to change the filter soon afterwards along with the oil.
Some companies such as Costco have gone to the Top Tier standards but do not pay for the licensing to be Top Tier. You might look into this as well. I don’t have a Costco near me but my parents do. They buy everything there including gas. The gas is quite a bit cheaper and they say the membership would pay for itself even if they only bought gas.