In terms of a "first" gun, a revolver is a strong consideration. However, I must disagree with an earlier response, in that revolvers are NOT easier to clean than pistols. Of course, this depends on what you consider to be easy. Consider that the pistol, besides the frame, has only the barrel to worry about cleaning, for the most part. The revolver, however, has the barrel and 6 to 7 cylinder chambers, in addition to the rest of the weapon, all of which will need cleaning. If you only fire the weapon once or twice a year..no big deal. If you fire it many times a year, the cleaning process could become tiresome. Plus, most pistols are much more easily "broken down" than a revolver. Revolvers, internally speaking, are practically like Swiss watches. You dont want to mess with them too much unless you know EXACTLY what you are doing.
Also look at capacity. A 9mm, as of now, will net you up to 16 rounds or so..depending on the gun you choose. I believe the most you will get out of a revolver would be 7 rounds. Now, for home defense a revolver should be more reliable than a pistol, but pistols these days have pretty much closed the gap on this concern. Not completely, but close. Keep in mind the reloading factor of a revolver vs a pistol. This is a particular consideration when either one of these are used in a home defense situation.
Basically, it all comes down to you and what you feel comfortable with. Just be aware of the limitations and/or advantages of both pistols and revolvers. However, it is usually accepted that those just starting out with guns choose a revolver. However, going with a 9mm is also quite recommended. As a side note, if you go with a revolver, hopefully a .357 Magnum, make sure it is a large frame. Small to medium framed revolvers generally cannot handle a steady diet of full house .357 Magnums nor .38 Special +P ammo. This is only a concern if you actually plan on using such said ammo for home defense as it is always recommended that you practice with ammo you will use in a defense situation. Do some more research on the pros and cons...the answer will come to you! The debate of revolver vs semi-auto is a time honored one. You should be able to find more than enough information on this via the internet. Happy hunting!!