actually, i'd suggest neither. by the time you spend on bags or jars and shipping, you could have bought a really nice pressure cooker or autoclave/canner. once you have a pc, your contam worries are OVER! half pint jars are about 6$ for a dozen, so that's pretty cheap too.
as for the pellets, i think that would be more expensive than the alternative. a small bag of peat moss (sometimes labeled as sphagnum) costs 2-4$, same as vermiculite. 72 jiffy pellets is now around 6$....
really, a pc is your best bet to jars. grains are awesome vs cakes, as grain to grain is an option then, and colonizes faster than a lc inoculation. i use corn, and soon to start spawning to cow poo and hay....