I think the designers felt that the strength of Life Imagined will come from how the runner has to keep in mind all three possible identities and play around them. However, I imagine that most people will be playing it with the Greenhouse ability active because, far as I can see, that's just the strongest. Let's take a look why.
The Brewery allows you to kill the Runner if he ever ends his turn with 1 card in hand. Now, this isn't a really common scenario because very few Runners will ever go down to 1 card against Jinteki. Sure, he might have hit a Komainu or a Snare on his second last click and not have enough time to draw up, but the chances of that happening don't seem to be large enough for me to warrant putting the Brewery on the flipside.
The Tank allows you to reset the game if it's been going on for too long and you want all your cards back into R&D. I'm... not entirely sure it's absolutely necessary, especially since this is a 45/15 deck. Of course, maybe you can use this to setup some sort of crazy Power Shutdown combo-wombo play, but aside from that, the Tank's ability is similarly too rare for it to be worth your ID slot.
Now the Greenhouse, on the other hand, lets you do all sorts of things. It allows you to bring a Project Junebug protecting your Shell Corporation to a guaranteed kill range; instantly score a Nisei MK II/House of Knives/Philotic Entanglement; gain a shit-ton of cash with Thomas Haas/GRNDL Refinery; or maybe just instantly power up a Ronin/Reversed Accounts and ready it for the kill next turn. In fact, if you spring for Biotic Labor - and Biotech seems to be built for click-gain effects - you can Biotic, flip Greenhouse onto a Ronin, and instantly use the Ronin to kill any Runner with 2 cards or less in hand.
The strength of the Greenhouse is that it is versatile. Unlike the other two flipsides, the Greenhouse can be used to spring a great number of nasty surprises on your foe in the form of traps, economy, or fast-advance. It is a great identity, and the fact that the other two flips may possibly exist is just icing on the cake.