Other then similar pricing and being lumped together in "sports watch" category, they are quite different.
The Breguet is a real scratch magnet and unyielding, but it has lotsa of presence, and a bigger date window. Also a point not very much discussed here, but a constant consideration for me....fakes...Breguet Marine, not that many fakes.
The Hublot is more sexy and fun. I don't know which one are you talking about, but Hublot competes in the space of oversized sport watches and it's more direct competition is the AP Royal Oak Offshores. The fact that you didn't bring up the AP ROO, hints to me you currently own one, or had some ownership experience? I am a fan of the Royal Oak, not so much the Offshore, but some are great. The Hublot BB is set to become a classic IMHO, but you must live with it's constant reinterpretation and variants, from material science to limited edition marketing....I know MANY Hublot owners who are turned off by this constant non stop limited edition marketing, myself included. I have sold off all my Hublots, keeping just the Manchester United and am on the list for another Manchester United watch, so I guess the marketing crap does work- however much we rubbish it. Also, there seems to be an increasing number of Hublot fakes, not good copies, but from a short distance, can't really tell. Hublot is a victim of it's own success here, and not helping themselves by having so many variants that the fakes out there can easily create something, and no one knows for the better!!!
Movements wise, I don't think they are of great merit for either, and the Hublot is probably machined finished, whilst I can't comment on the Breguet since I never owned a Marine before.
Practical considerations like power reserve, complications one get for the same price, even material. That could be your ultimate deciding factor.
Best,
Horo