I went through this question when buying my lift...I ended up going with a 2-post w/ overhead cabling and haven't regretted it one bit.
Assuming you have the floor to support it, 2-post hands down. Think about the typical work you do on a vehicle and how much of it requires working with the wheels removed, something that is easily done on a 2-post. If you're worried about stability, pick up a couple jacks from harbor freight. To me, the only advantages a 4 post offers is ease of car storage and quicker oil changes.