A locked N factor of 12 might work well. With an N factor of 12 it should be very hostile to GPU/ FPGA/ ASICs.
http://yacexplorer.tk/graphs.htm#tech
Both are already mined on gpus since day 3 of launch iirc.....
Also it looks like they are designed to give massive numbers of coins to the early GPU users initially then maybe eventually lock out competing GPUs leaving those early GPU people with massive haords in case someday the things do actually become valuable.
As GPUs advance 12 might not continue to block them out so maybe it would be better to start at 14 or more especially if going with a fixed forever value?
Still in the long run wouldn't they just end up as botnet coins? And because they are mined with general purpose equipment, very hard to secure since it is hard to have more general purpose equipment than the rest of the world has? Even with scrypt it might be too hard to have more hashing power than the rest of the world has if FPGAs and ASICs cannot really do a whole lot better than GPUs, so the classic merged-mined SHA256 coins (including bitcoin) look better to me every day.
-MarkM-