I voted submerged in water. I like to use diluted hydrogen peroxide.[1] I saw a forum post elsewhere[2] that a grower germed seeds in different dilutions and found 1% worked best. I wasn't that aggressive, so I use 0.5%.
I've never tried plain water. But, I like the concept of h202. The extra oxygen molecule seems to cause air bubbles to form on the seed, keeping it on the surface of the water where it's exposed to air (in addition to pure oxygen attached to the shell?). It's also a disinfectant.
I've had 100% seeds pop in 18-36 hours. If one took longer I'd feel less concerned about the seed drowning due to what I mentioned above.
[1] 1 part common 3% h2o2 mixed with 5 parts water, which makes 0.5% h202.
[2]
http://buymarijuanaseeds.com/community/threads/peroxide-for-germinating.147077/