Been a while since I've been on here but 28 years of doing nothing but selling and servicing industrial pressure washers makes me an expert in this field (nothing else though lol)
As someone stated there are 3 categories.
Cold water. Great for residential cleaning, houses, decks, concrete, knocking off mud etc. Electric or gas, doesn't matter, its all about horsepower. The problem is, 110 volt current will only give you 1600 psi @ 2 gpm. Give me 220 volt current and I can duplicate anything you can do with a gas engine.
Hot water. If you have grease or oil, its the best way to go. Equipment, trucks and also commercial sidewalks for chewing gum, its your only choice. Again, gas or electric makes no difference. Note, hot water machines heat the water up to between 170f to 200F.
Steam, often used synonymously with hot water (but wrong) is 300f at up to 300psi. It is great at degreasing without soap but not used much as it is slow and you can't see what you are cleaning. Also, it is dangerous as you can get burnt easily with a hose failure.
To the OP's question. Most folks for home use are happy with a cold water washer. Note, heavy grease requires hot water, but light oil is cleaned fairly well with cold. Soap is an important and oft neglected part of the equation. You will never clean black streaks off gutters without it, whether using hot or cold. And decks should always be pretreated with a deck cleaner before blasting away,,,,,,,,,,,,,,unless you like raised grain and a splintered surface.
There are 4 components of cleaning and while the order may change for certain jobs, most will fall in this order. 1. Chemical 2. Heat 3. Volume of water (GPM) 4. PSI Unfortunately its much easier to sell PSI and that is what everyone looks for.
There is no reliable pressure washer new available for less then $700 or so. The cheaps $100 to $400 machines will not last and are nonrepairable.