look here too
Before you do anything, read and make sure you understand about how your tank will cycle.
If you understand what that term means and what to do and what NOT to do, then you will enjoy keeping fish. If not, then you will be posting questions like "Why do my fish keep dying?"
If I were you, I'd go with the 29 gallon and an Eheim canister or a Cascade filter if you want to hang something on the back. Then get a Coralife compact lighting unit and a glass top. DO NOT waste your time with the standard hood. It's not enough light.
Don't be lazy. Be prepared to do regular water changes. It's isn't a huge deal to do, but you will have all sorts of water chemistry issues if you don't, and that's life or death to your fish.
You will need to have and use a water testing kit that measures pH, ammonia, and nitrite at the very least. If you do water changes, then nitrate isn't a big deal, but if you have the test kit for the above, then nitrate will be included. It's useful if you have a planted aquarium to know what nitrate is, because plants will take it up. Not as critical as ammonia and nitrite though.
Don't forget that you will have to dechlorinate your water if you get it from your city or town. Well water doesn't have chlorine of course. You will kill your fish if you do not remove the chlorine.
Once upon a time, chlorine was used, but now longer lasting compounds that bind chlorine to the water are what you'll find coming out of the tap. Chloramines and such don't evaporate, and you'll have to chemically neutralize them. No biggie, but you must remember to treat.
Someone mentioned snails. Snails are a PIA, because they can overrun a tank. There are exceptions. One are the Nerites. They are often found in marine tanks, but freshwater people use them too. They will do fine, but they won't breed in freshwater, which IMO is perfect. They can be quite attractive on their own. Nerites are
beautiful creatures in their own right.
Do be careful about what fish you select. I would avoid Walmart like the plague, as well as other large pet chains. Mail order is fine, and you can probably find reviews of local pet stores. In any case, find a store and go in and look around. If you see a fish you like DON'T buy it. Go read up on it.
African cichlids are beautiful fish. So are South American rams, also cichlids. If you try to keep them together, something will die. Why? Because the former need hard alkaline water. The latter need soft acid conditions. They are mutually exclusive in the same tank.
Then there is the question of temperment. Some fish just don't get along and will kill others of their own kind. Others will suffer unless kept in groups of half a dozen.
Sometimes one fish becomes anothers meal. You don't want that grief, so read, read, read, and THEN set up the tank. You'll not become discouraged and "wish you knew then what you know now". Don't be "that" guy.