Would you expand a bit - have you reloaded for 6 creed also? What made you choose 243win of the two?
In fairness, no, I don't have any first hand experience with the other 6mm cartridges beyond 243 Win. My dad bought me a 243 Savage 110 and a Lee single stage press for my 19th birthday. So that's how I chose 243. (My dad shot competitively and hunted with a 243 pretty much since the cartridge's inception.)
What I like about 243 and why I've stuck with it for over 25+ years: I like the lack of recoil compared to 30 cal cartridges, yet it pushes enough velocity and has enough BC to buck wind at longer (300 plus yards). For purely target shooting (as I mentioned, I ran mine in High Power for a few years), the lighter bullets do extremely well. (60 grn SMK HPBT with 4895 was my preferred, and that would do 5 shot groups into a ragged hole at 100 yrds.) For a hunting gun, it has a broad application from varmints to caribou. (I know of people who have taken moose with 243.) With the advent of Barnes TSX bullets, it becomes even more useful. Lastly, to some extent, it's what I know; why would I move to some other 6-6.5mm cartridge?
What I dislike about 243, and I suspect this might be an issue with other 6-6.5mm cartridges as well, is that the bullets, even the heavier 100 grn projectiles, tend to be quite fragile, especially at the higher velocities of 243. Thus, in a hunting application, if your projectile encounters even a twig from a branch, they the bullets tend to break or at least deflect easily. It's not a good brush gun caliber. The other shortcoming is, as others have stated, is barrel life; 243 tends to erode barrels more readily than do 30 cal cartridges. But i have to say, that I haven't seen a significant negative impact from this yet, but it's probably on my horizon. For most people, I doubt it will be an issue.