If I wanted DM, should I... (in General)

Train it on my 1st minion, making my 2nd minion AS really strong backed by RoS while the 1st minion AS is very weak...
or
Train it on my 2nd minion, making both AS's relatively close in size.
or
Even bother with DM?

1st of all, my AMF is not very significant. So my main spells are GA and AS x3 (RoS counts as a 3rd imo). DM would allow me to knock out those silly VA's that counter my GA pretty well. It also lowers enemy AS's for my Guardian Angel's to kill more easily. Takes out SS to lower the effectiveness of AC against my GA. However, this means my HP will be lower.

Do the pros outweigh the cons?

If you decide to train DM then you should train a lot of it or just enough to take care of the smaller EDs.

You want your AS sizes to be as disproportionate as possible to mitigate the effect of DM.

Ok, so since I need as much HP as I can get I suppose I'll just make a small DM for the small ED,s like VA. Thanks