I recently stopped drinking diet sodas a few months ago. But it wasn't the soda I was craving it was the carbonation especially with a meal. I switched to some variation of carbonated water (sparkling, soda water, etc...) You still have to be careful though, there are some carbonated water that use artificial sweetners. Crystal Geyser Sparkling Mineral water is good option. There are many flavors when you get them at Costco in bulk. When I'm at a restaurant I usually ask for soda water with a lemon wedge.
Spike in sugar levels in the blood cause hunger.. HFCS in regular sodas are 45% sugar 55% fructose. The fructose goes directly to the liver, were it can cause damage if in high concentration, similar to alcohal. the sugar is dumped into the blood stream and will cause an insuline reaction. This is also bad. The spike in blood sugar causes hunger.
Caffiene isn't that bad, but it has been known that diet sodas inhibit weight loss. They have nnothing to do with hunger. Well drinking more water actually supresses hunger, so carbonated soda is about a 4 to 1 ratio when it comes to water. Meaning if your dehydrated, it will take 4- 8 oz cans of cola to equal 1 - 8oz serving of water. So if you drink like 20 cans of soda you might become less dehydrated.
Just drink water, if you want flavor, drop in a lemon or something.
If your going to need Caffiene i would go with Cofee or Tea.