Keep and mind this is asking for the best element for deckout - which means reverse time does very little to help win by deckout.
The eternity is nice against the rare opponent that is also running a deckout, but not necessary at all for a deckout deck.
^^This. Lots of people thought only of Eternity lockdown, but we're not talking of decking out a FG (I don't think any mono deck can deckout a FG consistently), we're talking of deckout in general -don't we?-.
So I say or , for great CC, even though is better, since Antimatter is both CC and healing, and Antimatter+Dissipation Shield lockdown is so cool
But in a deck out game the opponent has one or two growth creatures such as Lava Golem, Vulture, ect. which (after long enough) can go beyond regular CC. The best solution for growth creatures/buffs (which can also come up in longer games) is... ETERNITY!!!
After long enough, Antimatter would create a -20 creature. Before long enough, Chaos Seed and Pandemonium are awesome, they can freeze, REWIND, attack, poison or even TU the creatures. Also, Fire has enough CC to deal with anything, except some REALLY SLOW high hp creatures (Gravity Dragon, mostly unused, and buffed Armagios/Vodoo Dolls, but the most common buff is Rage Potion, that already makes them killable).
So meh. Time sucks by itself.