Are you hoping to get a new AC system in place before the summer heat begins? Or did your current system break down beyond repair? In either case, you need something new, and you need it very soon. The main options that you have are to get a window unit, portable AC unit, or to have a whole central air system installed in your home. There are many factors that will determine what you will choose to do in this situation, and we can lay out those factors for you right now.
Let us start with a situation where you are renting a room in a house, or you live in an apartment. Central AC is not an option in this scenario, unless it already exists where you live. The best you can do is choose between a window and portable unit. If you have windows that slide up and down to open and close, then a window unit is your ideal choice. It is cheap, small and will cool down a small to medium-sized room very easily. The only issue is that it will look a bit ugly sticking out your window. But if you do not care about that, you are good to go!
Now what other options do we have? The second option is the portable unit, which is necessary if you have the windows that slide sideways. These are more expensive, but they will still work pretty well. They cool nicely, and you can slide them from one room into another if you stay in multiple areas of the house during the summer.
In terms of central air, it is only an option if you own or rent a whole house. And even then, you will only want such a system if you are living in more than one room in the summer, or there are many people in the house and you all need AC!