It's called ZekEels, so Zekrom. Zekrom is a staple, Thundurus is good, but it's not necessary. The format is much more aggressive now. It's not that hard for the opponent to KO Thundurus before it takes a prize of its own.
ZekEels is based around the regular BW Zekrom. Zekrom EX was just a nice addition for the deck allowing you to hit for over 130 damage (i used Raikou & Suicune Legend before its release)
If you're running Zekrom EX then just keep it at 2 as it can be a strain on energy. You should only be using it in situations where you feel you can take continuous prizes (2/3 prizes usually) or to OHKO other EX's, otherwise just use the regular Zekrom for everything else. My list runs just 2 Thundurus as it isn't too important but starting with it and going first puts you in a good position.
3 Zekrom
2 Zekrom EX
2 Thundurus
My list originally ran 4 Zekrom BW but i dropped it to 3 for DCE.
Well I'd call both regular Zekrom and the EX a staple in the deck, but the name came from the regular Zekrom. In HS-NV, ZekEels existed as a deck, but Zekrom-EX wasn't in the format.