I prefer White Sun's Twilight as the Phyrexian Mites provide a unique axis of pressure, but a deck thats interested in one will likely run the other
the former earn you coins you can then use on boosters, while the latter can be used to create or clone cards to fill a deck rather than chancing it with booster packs
Using several cards like Vito, Thorn of the Dusk Rose, Vizkopa Guildmage, or Sanguine Bond can turn your huge lifegain into huge life loss for your opponents
This is pretty negligible, for every one drop you run, just on the maths, you can run two two drops
Most decks run about 1015 Energy cards, depending on how fast you want to go and how much Energy your attackers need
8 Stormcatch Mentor A Better Goblin Electromancer