to 51% myriad afaik. you would need 51% of each algorithm (technically only 20% or so is required for a chance of success. 51% is pretty much guaranteed (thats how wdc got attacked))
and selfish mining from what i know would just cause the selfish miner to fork due to the requirements to have the other algo's
Ok, so I take it as yes, myriadcoin is technically more secure and less easy to attack compared to bitcoin.
However, it has 5x or greater risk of an algo being compromised mathematically (groestl, qubit and skein are still somewhat experimental, right?)...
Although I suppose the coin could be hardforked if such an event occurred?