Hi kpauley,
First, congrats on getting yourselves certified, and welcome to the sport!
Be careful of rushing out and buying all of your gear immediately. The two BCs you mention are very different beasts. The Oceanic Cabo is a jacket style BC, and the SeaQuest Balance is a back inflation BC. Which style did you dive during your open water course? Most likely it was a jacket BC. However with some experience you will rapidly appreciate the improvement in streamlining and trim that comes from a back inflation BC.
Back inflation BCs promote a more horizontal swimming position in the water, which presents less drag and less expended energy, which helps for a more enjoyable dive. Most technical divers use back inflation BCs or a similar concept known as backplate and wings, because of the improved trim and streamlining over a jacket BC. It may feel funny at first being in the face-down swimming position, but you're usually looking at stuff on the bottom anyway
People sometimes say that back inflation BCs present a drowning hazard, as they tend to push you face forward into the water on the surface - which is a load of bunk. Just lean back against the BC on the surface with your legs out in front of you, instead of bent beneath you, and it's like a big comfy armchair in the water.
Your LDS may or may not have both styles of BC available to rent, but if they do, DEFINITELY try both styles out (on the same day if you can!) and see if you prefer one over the other. Note that SeaQuest has several women-specific BCs as well (including back inflation), which your girlfriend may find more comfortable, depending on her body shape. Hopefully your LDS could work out a specific package for her.
SeaQuest BCs and Zeagle regulators are both fine products - Oceanic tends to be more entry-level, and is often just generic gear rebranded as Oceanic. Not sure about the specific Oceanic products you've mentioned though. The SeaQuest BC will also hold its value better if you decide to sell if for any reason. Also, both of these BCs will only take a single tank - if you're just beginning your diving career, diving with double tanks is a long ways off yet, at which point you would want to look very hard at the backplate and wings. Incidently, a backplate and wings for recreational diving would cost about $500-$600, but would be an investment you would not regret (but you didn't ask about them so I'll shut up and stop confusing you!).
Hopefully other people on the board can offer some advice on the regulators.
cheers
Ben