Well, Prussia is definitely the boarding faction; they have the best numbers of
AP. They also benefit from having a Sky Fortress, which in addition to looking totaly awesome is also a very tough nut to crack thanks to its ability to go obscured.
The Brits are a very torpedo-heavy faction. I haven't used them at all, and only played them a little, but the general consensus is that they are a bit underpowered (at least with a fleet of the currently available models).
This thread here (from the Spartan forums) has a lot more detail:
http://forum.spartangames.co.uk/smf/index.php?topic=6247.0