Straight.
I've found *very* few cases where serrated edges are more useful than straight edges, especially a very sharp straight edge. I tend to consider serrations a specialized edge best used for specific situations.
For example, it's often thrown out that serrated edges do better with cutting rope, and I won't deny that they do, but for *most* rope cutting, the difference is negligible. Personally, I've never had problem cutting rope with my non-serrated blade. However, I am aware that some types of rope, especially certain "high tech" poly ropes, can be difficult to cut with a straight edge, especially when they're wet. Since I don't deal with those on a regular basis, I consider that a special case.
At the same time, however, I've found a number of cases where serrated edges fair worse than straight edges. Add in the significantly greater ease of sharpening and maintenance you have with a straight edge, and I rarely bother with serrated blades. The same goes, to a slightly lesser extent, for combo edges. I generally don't have much use for them. There are a few situations where they might come in useful, but not nearly enough to get me to carry them regularly.