So consider which god(s) you gain access to via the seeded pack, as that's the best chance you have of pulling a mythic. Red and green will get potential access to Xenagos, while red also has potential access to Mogis... seems then, that the best option for a first go would be red. But, if you consider that half the pre-release pool is Theros, white has Elspeth... and well... she just beats everything in the set....
The Seeded pack that is actually influenced by your color choice likely wont have theros cards in it though will it?