Ok... Big is always better; more water is more forgiving of mistakes. Of course bigger = more money and that is also a factor. A 55g is a good size for most needs, 70g even better. That gives you lots of flexibility in fish. If you're not sure about the hobby, then start with a 30g (30") or a 40g (36") which will be less expensive.
If you're interested in cichlids, you want something hardy and easy to deal with that doesn't get too big for the tank. Here's where the tank size is going to dictate your choices. Additionally, you have to decide if you're willing to deal with aggressive fish (where you may get injuries, stress illnesses, or deaths). Next you have to consider (realistically) how much time and energy you want to invest in the fish. Some fish take a lit of effort (Discus for example). You also need to decide if you want breeding to occur (you have to find a place for the small ones, and this may lead to some aggression).
I don't know anything about African cichlids, but they are a good choice for color and appeal, and others can help you.
Good choices in New-World cichlids: Angels of course, keyholes, festivum, convicts are a no-brainer; they stay small, are hardy, and will breed easily (assuming you want that). Firemouth get a little larger, but not huge. Rainbow (multispinosa) are a small, calm cichlid. There are a little more rare possibilities: sajica, honduran red points. Mind, you cannot just throw all these together!
With a bigger tank (staying with calm fish), you can get into severum, nicaraguense. If you'll tolerate some aggression, you can look at dempsey, green terror.