I think block is less expensive and less time consuming.
When you pour a wall, it takes a lot of time to "form it", and you must reinforce it. Plus its solid so you are using more cement ($$$). Its more succeptable to cracking with expansion and contraction so the length of a segment is limited. However, walls are usually poured when "strength" is a consideration. A poured wall that is properly reinforced could probably support 20 times or more the weight of the same size and thickness block wall.
The 20 times # is a rough guess. If you need more accurate data, contact a structural engineer, or goto a good library at a college that offers structural engineering.