I've ridden Gatorskins, GP4000S, and GP4 Seasons in 25mm.

The Gatorskins are fast and ride well for tires that puncture resistant and long lasting (not bricks like Specialized Armadillos) . In absolute terms they're not that fast or nice.

The GP4000s ride nice and are fast. They are not long lasting.

The GP4 Seasons are an answer in search of a problem. They ride fine, but are slow tires and last half as long as the Gatorskins. If you're OK with the lifespan you want the GP4000. If not you want the Gatorskins They might make sense if you plan on racing in the rain where corning a hair faster than with GP4000s (which are stickier than the Gatorskins) would help you win, although if you're like me and in no hurry cornering in the rain (going over a manhole cover or cross-walk stripe can really suck with some speed) you're not going to stress your tires enough for the difference to matter.

The GP4000s and GP4 Seasons don't seem to flat appreciably more often for me than the Gatorskins (which is rarely). The GP4 Seasons and Gatorskins do have more sidewall protection which might matter in situations like gravel.