I had the Festool PG set. They worked well, but as soon as the Seneca PGs became available, I bought those and sold the Festool guides a month later, after I figured the Seneca guides had proved worth it. The design of the Seneca guides made more sense - to me, at least.
With the Seneca guides, I set them and lock them in place. As long as I set them on the shortest piece I'm going to rip, I can simply move the guides on to the next piece - no need to even touch the guides. The Festool guides need to be moved so they span the length of the rip. No big deal if you're ripping a bunch of the same length stuff, but it's a nice advantage sometimes. Say you rip a full sheet down, then have some (less-than-full-length) scraps you also want to rip to the same width - you'll ed up moving the Festool guides for each length of material. Also, since the Seneca guides don't go under the rail, when I go through a batch of the same length stuff, I can use the Festool rapid clamp.
The Seneca guides also ended up being cheaper - I sold the Festool guides (used) for quite a bit more than the Seneca plus Incra track cost.
There was one time recently when I think the Festool guides would have been better, but I can't remember the circumstances. I wish I could remember, but I mention this to point out that even though I prefer the Seneca guides, I recognize that the Festool guides might be better in certain situations.
The floppiness of the Festool guides would sometimes bother me, but that wasn't the reason for changing. The extensions helped, but I didn't always have those on because they made it a little more awkward.