I've skated on Gold Seals and 99s (never coro aces, though, I was in Phantoms as a youngster). They are very, very different blades!
Pattern 99s are very low to the ground, and have much shorter tails (though larger toe picks). In essence, there is much less "blade" than the Gold Seal. I think they are a little easier to control on turns for a few reasons - less blade, less to move, less of a lean is needed to hit a solid edge. I prefer toe jumps in them, the pick is very secure. There is less 'glide' with these blades, though.
I ultimately stuck with Gold Seals because I frankly couldn't spin worth a damn in the Pattern 99s. The rocker on the Gold Seals is pretty severe in comparison, and requires a shift further forward to find the spin rocker. Edge jumps overall felt more secure to me. I also felt much easier lift on my axels in the Gold Seals, and I think my speed is a bit better. They do require more precision than the Patterns, IMO.
I hear that Coronation Ace to Gold Seal is an easier transition to make than others, but most of the kids around here go from Coronation Aces to Pattern 99s. That's definitely the most popular blade with the younger set in my area right now!