Like everyone mentioned, the 2-post if you are working on the car daily like in a mechanics shop, or the 4-post for storage, and flexibility.
By flexibility for the 4-post, The concrete can be standard thickness and strength, and with a wheel kit they are pretty easy to move around. You can also get under the car with the cars weight on the suspension to tighten all the suspension parts and do alignments (if you have the tools?) For storage, you can place drip trays or plywood between the runways to keep drips off the car under the lift.
The bad part of the 4-post is always having to duck under the runways, and needing a jack bridge or tall axle stands to lift the wheels off the runways to do brakes.
With either, the accessories make them better, like a good trans jack and the rolling oil drains that hold 15-20 gallons of fluids. I have one for oils/lube and another for antifreeze.