Every type of algo has it flaw. What is nice with the myriad is the possibility to include five different algos so the inherent flaws somehow equilibrate.
I think we shall go to one ASIC oriented algo (scrypt), two or three GPU aimed algo such as Lyra2 and Myr Groestl for instance and finally one or two CPU aimed algo such as cryptonight or prime-constellation (http://riecoin.org/faq.html#pow). Five algo is good with 1 pro-ASIC, 2 pro-GPU, 2 pro-CPU.
Also Cuckoo cycle looks interesting for a CPU algo too https://bitcointalk.org/index.php?topic=707879.0
If cuckoo was ready seven algo could even be possible in the myriad: one ASIC (scrypt), three GPU (Lyra2, Myr Groestl, Skein...), three CPU (cryptonight, prime-constellation, cuckoo)... network will be very resistant
also meeh like the number 7 
I would not put a multi-algo algorithm such as X11 or quark. For once because it is more heavy verification time-wise, second it does not bring anything new over single-POW algorithm (in contrast to a myriad like implementation ofc), third one of the algo can be flawed and the POW will be too, fourth as the miner in public domain are not optimized there are big player that can use custom miner to have more benefit, fifth there are FPGA raping X11 right now, sixth it was made by Eduffield and remind of darkshit.
BTW look what an optimised miner could do to unsuspecting miner using the non-optimized one http://da-data.blogspot.de/2014/08/minting-money-with-monero-and-cpu.html. I never understood why people prefer to use un-optimized miner thinking it economize their energy bill, this is retarded.
1% POS maybe, I am not sure, but no more. Indeed i am afraid it will incentive people to keep coin in ANC instead of in ZC, reducing anonimity set. This one has to be thought about if it is really needed or if the myriad is enough for network security. I would prefer a pure POW if possible.
CPU-only as to now: http://cpucoinlist.com/cryptocurrency-algorithms/
With the myriad the network will not be down for days anymore even if one of the algo is undergoing an attack
If the coin was to go for a myriad of seven chains then I would prefer two ASIC chains. With both SHA256 and Scrypt then three GPU chains NeoScrypt, Lyra2 and Myr Groestle or Skein (which ever had a larger networked coin to AuXPoW with). Then two CPU chains of Cryptonight (Monero) and Primecoin. An attacker would then need to control four of the AuXPoW chains to cause major problems.
Edit: Although seven AuxPoW chains may spread new coin distribution too thin on the ground? In hindsight a myriad of the three AuXPoW chains of Lyra2 (Vertcoin), NeoScrypt (Feathercoin) and either Myr Groestle or Skein (which ever had a larger networked coin to AuXPoW with) is my favorite option. Although moving over to AuxPoW with Litecoin is probably the quickest and easiest solution for now. Then possibly just Lyra2 (Vertcoin) and NeoScrypt (Feathercoin) AuXPoW can be added to make a myriad. As not taking into account X11 then those two networks are probably the largest GPU biased networks. So more network strength would be gained with the AuxPoW.