Timebomb. Classic 'Science meets Art' look while sporting a mecha-quartz movement. Frankly, for the money, especially these days, the TB is a much better buy.
Let's go down the reasons.
First of all, the TT is still in production whilst the TB is out. That alone adds reason to get the TB over the Tank for supply.
Second, the Bomb is sleaker design. It's also slightly lighter if you go for the non-ion plated models. I know that aesthetics are subject to personal opinion, but I think many people here would agree that the Bomb is more representative of a good Oakley era that doesn't really see much debate over whether or not it was good, whereas today there are those (myself included) who decry modern Oakley beholden to stake and stock holders. The TT was a design driven by an attempt to fan demand rather than a design that blossomed. I look at it and feel myself cringe slightly.
The TB movement is based on a Seiko/ Citizen eubache. Very reliable. The only downside is that it's reserve battery is ludicrously useless. I have no before hand knowledge of the Tank's movement but then I'm not one to be sold on a "chronograph" looking watch that is driven by battery.
Four: Here I am about to traipse into territory that will make people hate me and love me. The Timebomb is a first while the Tank is just a dying gasp. I have no doubts that the Tank keeps excellent time. In fact, I've read reviews and heard opinions on timezone.com that place it as one of the best buys out there for a watch of its price in class. However, it does not say OAKLEY to me. To me, Oakley is about Mad Science. Mad Science is best captured with designs like Romeo, Juliet, Plate, OTT, TimeBomb, Zero 0.3, etc. The Tank looks like something that Diesel could have made, or even Fossil watches. If I wanted a Diesel, I could easily go out and buy one. I want an Oakley and the Timebomb, Torpedo, and Crush are the watches that most suitably represent the design philosophy I love so much.
Point number five. Just you wait, the Time Tank will fall in price. As much as many of us would hate to admit it, Oakley does NOT make watches known for their luxury pedigree. These are not IWC Schaffhausen watches, Patek Philippes or Vacheron Constantins. They're Oakleys. They're not purely mechanical. Plus, the Tank is marketed poorly. Additionally, what poor marketing is done is aimed at segment of the population that the fine luxury swiss watch industry largely snubs its nose at: posing twenty-somethings. It's a good watch, but the ads really don't show that. The Timebomb did. The Bomb offered an air of exclusivity.
I'm hoping that my opinion will be read constructively. These are by no means incendiary remarks so please don't take them that way.