Get the Odyssey, I compared the Odyssey 3pack to the Regent and the Regent is more of a little sister to the Odyssey.
The Odyssey might have a slower turn rate but a more favorable bridge officer layout when it comes to tactical options, with Lt. Cmd. Universal used Tactical plus the Lt. Tactical.
For example on the Odyssey I can easily use Fire at Will 3 with Torpedo Spread 2 and Attack Pattern Beta 1. On the Odyssey I will either have to downgrade the Torpedo Spread, sacrifice the Attack Pattern Beta or forget all science options and use the Lt. Universal also as a Tactical.
Also with saucer separation the Odyssey becomes a real beast and superior to Excelsior or Regent.
And both ships are left in the dust by the Imperial.
Ok so I'm torn between these two vessels, I am leaning towards Odyssey cuz of the Aquarius escort and what not and cuz you know, it's the biggest starfleet ship yadaydayada.
Only problem is every bob and is dog has an Odyssey and I rarely ever see a Regent flying around...
Did I just answer me own question?
Get both... and by that, I mean both the Regent and the Odyssey PACK.
From the Regent, you get the Wide Angle Quantum torp. From the Pack, choose the Tac Odyssey (until such time as when Sensor Analysis mechanics get changed) and install the Work Bees (sci) and/or Chevron Separation (eng) consoles. I usually am content with just the Work Bees (used as a bit of preemptive hull repair) as dropping that much hull points for some extra turn rate... in PvE you should be able to think far ahead enough that you don't need to turn as much and in PvP... do you really want to give up that much hull points?
If I had to choose between the two, I'd go for the Ody pack.
A few other things you should know. As mentioned in the other replies above, the Aquarius escort is a mobile coffin. For that matter, the 'saucer' is not that much more useful or survivable. Both are marginally useful and frequently annoying.
The Ody is NOT the FED cruiser with the most hullpoints.
... and just in case noone tells you too... get another ship ^-^.