Though there is a lot that can be said about any of these different types of machines, today let's just take a look at cold and hot pressure washers, their pros and cons, to help you decide which type will work best. From there you can go on to look at different power sources and sizes when you take the next step in your decision process.
First let's look at cold water pressure washers. Cold washers can either have a tank to carry water or can be hooked up to a regular hose. This means that they can be smaller than hot water washers, and also that they start at a lower price point. These are great for around the home use, things like cleaning vehicles, siding, decks etc. They easily remove dirt and grime, much better than using a standard hose with just a nozzle.
As you can guess, hot water pressure washers are heavier and larger than cold water ones. This is because the machine has to have a tank and a burner to heat the water before it is used. Many hot water machines come on a cart, but there are also large, industrial sized ones as well. The primary reason you would want a hot water pressure washer is because it cleans better, especially any type of grease. You don't wash greasy pans in cold water. No matter how much soap you use, the grease stays. Hot water helps to break down the grease and wash it away. So if you are going to have to clean any grease or oil based products, then you need a hot water unit. Another nice thing about hot water units is that you usually have the option of running cold water instead, which can save on the extra gas needed to heat the water.
Basically, the pros of cold pressure washers are that they can be portable and lighter since they do not have to have water tanks, and they are great for removing every day grime and dirt. And in general they are less expensive. The primary con of the cold, is that they do not clean oil based stains or spills. Therefore, the obvious pro of hot pressure washers is that they have a wider range of cleaning capabilities. The cons are that they are often larger, heavier and more expensive.
So it really comes down to what you need to clean, if you are cleaning a garage floor where you do mechanical work, then you need a hot unit. If you are doing basic grime removal around the house, a cold unit will work. If you are a business, do the same type of evaluation. Once you know whether hot or cold water pressure washers will work best for you, then you can delve into your other options.