You probably need a fan to do one of two things:
Tower fans and their old-school grandparents, oscillating stand fans, have the same problem: they only move air within the room. If the room's full of hot air, all you get is hot moving air. And while it's slightly better than hot still air, there are better options.
Ceiling fans have the same problem, but they're nicer to have because they're usually less intrusive (unless you're really tall), much quieter, and much more effective at blowing the air around larger rooms.
What about double-blade window fans? They sound like a good idea: get the cooler air from outside into the room, either directly (by blowing in from outside) or indirectly (by blowing out from inside, therefore sucking outside air in through other open windows).
Double window fans have two main problems. They're primarily a pain to install, often requiring the same steps as window air conditioners: screw brackets into the window frame, stretch accordion panels across the gaps, and close the window around the unit. This is fine, until you need to remove it. Air conditioners are insulated from the outside for efficiency, but window fans are wide open around the blades, so you have to remove fan units in the winter (and sometimes if it's raining sideways). Generally, it's convenient to be able to install and remove any window-based items as easily as possible, especially if you don't have a lot of good windows to spare.
The other problem is more severe: they simply don't work very well. They don't move a lot of air, and they make a lot of noise not moving it. It's a bad design. For a given rotational speed (which corresponds directly to the noise level), one large fan will always push more air than two smaller ones. You're much better off putting one big fan in the window. This sounds like a job for...
The box fan!
Box fans are the most versatile and effective fan type. They're light enough to be carried easily around the house, they're relatively cheap, they last forever, and they can be placed almost anywhere: floors, tables, desks, and windows. And when you put a box fan in a window, you don't need to screw anything in - you just put it there, and easily take it out when you're done. Box fans put all other fans to shame.
Box fans are, by far, the best type of fan you can get to cool a room. And in my next article, I'll prove it to you.