The thing to remember is that a horizontal axis (HAWT) is inherently more efficienct than a vertical axis (VAWT). Put simply, this is because on the VAWT when a blade is at the back it is in the "shadow" of the blade at the front, and when the blades are at the side they are not generating any power at all. In contrast, the blades on a HAWT generate power all the time.

However, it's important to consider where you plan to mount it. If it's going to go on your roof then there's a special case - as the wind flows over the house it has a vertical component, rather than just being horizontal. In this situation a HAWT is less efficient than normal, and will experience higher stresses and therefore needs to be stronger. In contrast, the VAWT copes quite well with non-horizontal air flows.

Another important difference is that a VAWT is potentially easier to install as the weight of the generator/gearbox is at the base rather than at the top. However, this also means there is a fair amount of stress on the generator/gearbox bearings when a strong wind is trying to push the turbine sideways.

Finally, there's the obvious difference that you have to point a HAWT into the wind. The advantage for a VAWT is not just that it can be more simple, but that a HAWT can only respond so fast to changes in wind, and in a built-up area the wind is often gusty and turbulent.

Regarding the wind database you got the 4.4m/s from, don't base any important decisions on it. These databases are notoriously unreliable, especially in built-up areas. The only good solution is to put up a wind mast and data logger, ideally for a year, but any length of time is worth it. A cheap way to get one is to spend about £100-150 on a "weather station" that links to your computer. I have one at home that can store 175 samples of all data for you to download periodically. (Note that a real data logger would store thousands and only need downloading once a month or so)