I think there's a bit more to it than simply masthead vs fractional or asym vs sym. Hull forms, rig geometry, sprits, poles, weight all factor in. It's difficult to be categorical about either one - so much depends on the many variables.
For instance, there was a time when most fractional boats also flew fractional spinnakers (whether asym or sym). Now, it's not uncommon to see a fractional rigged sloop, flying a mast-head spinnaker. Some designs even fly a masthead asym, and a fractional symmetric chute. Lots of variables.
In my experience, asym chutes work best for cruisers that aren't following a windward-leeward course, or for sport boats that can get up on a plane and so take advantage of better downwind vmg (i.e. they sail higher jibe angles, but at faster speeds so the extra distance doesn't hurt them). Asyms can also work well for non-planing race boats, but usually only for long reaching legs (rather than a dead run downwind).
But sometimes, especially in light air, running deep with a symmetric chute works better. That's why from one race to another, certain configurations may seem superior than others.
As Joms said, fractional rigs come in a lot of varieties. Some are SO fractional they need running backstays to support the rig. Others are only moderately fractional, and use more conventional rigs. Some fractional rigs have big overlapping genoas just like masthead rigs. Some masthead rigs are designed to sail well across a wide wind spectrum with a non-overlaping jib.
I think one of the trends in rig design that I like, is the effort to get away from large overlapping genoas. You tend to see this more on moderately fractional rigs, that put proportionally more sail area into the mainsail. Also, with the mast typically stepped a bit farther forward, in addition to easier headsail handling, you also often get the advantage of being able to sail reasonably well, and balanced, under mainsail alone.
There are downsides, of course. One important one is that the fractional rig will likely be significantly taller than a comparable masthead rig - a concern for many with bridge clearance issues.
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Pacific Seacraft Crealock 31 #62
NEVER CALLS CRUISINGDAD BACK....CAN"T TAKE THE ACCENT