Out of your two choices I would personally go with the surge/battery battery backup made for computers.
This is the battery backup I have at work... and I plan on getting one for my tank (I believe it was around 200 bucks at the Best Buy here). I don't know how long a couple of powerheads will run on this thing... but I'm pretty sure it'll run for a very long time, since this thing is rated for around 75-110 minutes on a standard computer setup. Obviously a couple of powerheads don't use a fraction of the amount of power a computer uses. The good thing about this kind of setup is that it provides surge protected outlets for things that don't really need a battery backup (ie. protein skimmer pump, lights, etc.). Surge protecting your electrical devices is not needed, but its nice. To top it all off, if the power goes out, or the breaker for that outlet trips, the battery will make a nasty wailing noise to alert you.
Its expensive to buy, but I believe in the long run it will be more cost effective. Its fully rechargable, so you won't have to replace the battery for a long period of time, and it has a pretty long life. I had an older APC battery backup run for a good 10 years before it died... fixing it was a breeze too. I took the thing apart, and found out it ran on some sort of motorbike battery... 40 bucks and 2 days later, a battery place got my battery in, and the APC was back up and running like a champ
-Richer