I judge energy counts based on what you want your deck to do. If I play a deck that has no energy acceleration or ways to move and maintain energy ( 1 hard attachment per turn) then at least 14 energy works. This all depends on how heavy the attack cost are. I use the EX legendary birds in my deck and they require 4 energy to attack but I also use a strategy that keeps energy in play so I can get away with 12, though 14 would help.
If you are using a deck that dumps a lot of energy a turn on to attacks, decks like Blastoise and Emboar, then 12 works fine. With the release of Prof Letter, letting you grab 2 energy from the deck (a lot better then Energy Search) You can play little energy, but have faster ways to get to them, allowing for more use of other cards. If you want to play a deck that requires trainer and attack based energy acceleration, 14 works because you need to see the energy first before you can do anything with it.
At the end of the day, this all depends on what attackers you choose and how you run the deck. I hope this helped and good luck.