I bought a 2 post lift a year ago. I have a good friend who has a 4 post, so I have done work on a variety of cars on both. My experience is that the 4 post is much better for parking/storing cars, but I like my 2-post better for working on them.
The advantages to the 2-post (for my usage) is that there more room underneath because you only have the arms instead of the ramps. It was great for an engine drop, because I didn't have to worry about fitting the engine between the ramps when I dropped it. It is also nice for bleeding brakes, etc. because you just raise it and then can take all four wheels off right away. With the 4-post, once it is in the air, then you still have to jack up the car to get it off the tires.
In addition, my purchase was budget conscious. I bought this one:
UnitedProducts TP09A Two-Post Lift
for around $1600 delivered using the "special pricing button." I have been using it for a year now and I it seems well built and I am completely satisfied. I am sure others (Bendpak) are probably better built, but for my purposes and my ocassional usage, I didn't want to pay that much.
Finally, with a 4-post, keep in mind that in addition to the price of the lift, you may want to get an addional jacking unit to jack up the car on the list, which also adds to the total price.