Put a lot of thought and planning innto my lift purchase. My garage addition was designed around this feature. So I really needed to get it right. I went with a four post for many of the reasons mentioned in these posts. Thought it might help to sum them all up in one place:
1. Storage is a big issue. I have a few unibody vehicles. So supporting the vehicle on the tires is important.
2. Safety... Two posts lifts are for professionals. All too easy to lift cars improperly. An improperly balanced vehicle is a disaster waiting to happen. I know a couple friends, one with a professional garage and one weekend warrior who let people use their two post lifts and had cars fall off. I agree that anyone with a reasonable degree of common sense shouldn't have to worry about this.
3. It has been mentioned here... But not having to get down on your hands and knees to set the lift is a plus as you get older. Coming home and from a cruise or show and not having to kneel on the floor when wearing clean pants is a big plus as well.
4. If you can only have one lift, the four post equipped right represents a great compromise. A sliding jack makes these things very versatile.
Considerations:
Capacity: Consider what you will be lifting now and what you may want to do in the future. I'm a cruiser. I'm not into larger trucks or motor homes. So 8K which seems to be the standard rated capacity these days is just fine.
Size: Bigger isn't always better. It sounds good to go with a lift that can handle a longer, wider vehicle... But this also increases the footprint of the lift and that takes up valuable real estate. It also makes the lift tough to get around in a tight garage. Same as above... Buy what you need. I found that my Econoline pickup with 10 inch wide wheels in the back would just fit on a Pro Park 8. I had thought that I would need a Bend Pak HD9 to accommodate greater width. Using the Pro Park saved me over a foot of floor space and a fair amount of money in the process.
Options: It's hard for many of us these days to spend the money on a luxury such as a lift. Perhaps even tougher to convince the wife to go along with it. But I have become an advocate of spending a bit more if it really makes a difference. Buying a sliding chassis jack was my best decision aside from the lift itself. I mentioned the versatility factor. A four post without this accessory isn't anywhere near as easy to use when it comes to many typical car repairs that require the wheels to be lifted. As many people have said here... Don't buy two. It's really easy to lift one end and place jack stands in place and then move the jack and lift the other end. The other consideration is that they take up a fair amount of room and two will really obstruct access to the underside of the vehicle. BendPak has the air operated jack. It's more convenient but much more expensive as well. I found the manual hydraulic jack to be just fine. In less than 30 seconds, you can have a vehicle off the runway and ready to work on.
Installation: I am reasonably hands-on and I am an engineer by trade. Certainly could put a lift in and I have installed much heavier and more complex equipment in my career. I elected here to have the lift installed. I bought it at Greg Smith and asked them to recommend an installer. I also purchased a very substantial two stage compressor from them (800 lbs). The installer picked up both items at their location in Delaware. transported them to my house in NJ and installed the lift. I figured it cost me about $200 or thereabouts to have the lify installed if you back out the freight I would have paid for both items. Well worth the price.
Construction Prep: I planned where the lift would go in my garage. I drew everything out. The garage, the lift, vehicles on the lift, lift raised. Checked my clearances every which way. Knowing where the lift would be, I poured the concrete in this area perfectly level. The result is an unbelievable stable and smooth lift. No vibration. No leg wobble. You would swear it is bolted down.
In short... One of the best investments I've ever made. I see all the arguments about where the lifts are made... Whether they are certified or not certified, etc. I searched locally for a used lift for over a year. Not much popped up other than commercial stuff that was simply too big for my garage. Buying a domestic hobbyist lift for twice the price simply wasn't going to work either. As a rule, I buy American cars knowing full well that a substantial number of components may come from other countries... But I do try to stick with American companies. My choice here was having a lift or not having one. I'm okay with the choice I made. Buy a lift... You'll wonder how you ever got along without one!
Might not want to engage the 4x4 with a size difference that big 
