freestyle vs breaststroke which is better?

Walking is easier.  Think I'll do that in my next tri...

Sorry for the smart red bike response, but IMHO breast stroke if done correctly is not easier than freestyle.  The breast stroke that you and I do, as opposed to breast strokers, isn't really breast stroke,  it's more rest stroke, as it allows you to regain your bearings, get your breath back, etc.

Reason #1.  It's faster. 

Freestyle means any stroke you want to swim.  Front crawl is more efficient (distance per energy expended) but it does require something of a moderate-to-high effort to perform whereas breastroke can be done at very low effort. 

Think of it this way.  You can expend 100 KJ and swim 1000 meters front crawl or 800 meters breastroke in 20 minutes (5 kJ/min).  You could do breastroke at 1 KJ/min (obviously much slower), but it may be hard to do front crawl at 1 KJ/min.  (These numbers are for illustration, I don't know how many KJ would really be expended with either stroke.) 

For triathlons, you also want to save your leg muscles for the bike and run. 

Absolutely freestyle...I use the breast stroke for a quick 15 seconds of sighting and active recovery during a race, but what they all said above! 

When going under a wave while swimming out when in the ocean: breaststroke

At all other race/open water swims- freestyle is by far the way to go.

I don't remember where I read it, but breaststroke (at least done correctly) is actually the most taxing on you in terms of energy required or something (I really don't remember the details but basically it was something to the effect of for the same distance, swimming it breaststroke is just going to require more calories- surprisingly not butterfly which most consider the hardest to do strength-wise).

Do some breaststroke in at least some of your workouts (there are some benefits of not just swimming freestyle in workouts) and it can always be a backup/rest stroke during a race.  But if your going to stick with this sport, you need to comfortable with freestyle. 

You can also basically swim a little of your workout (like a 100) with your head out of the water the whole time (basically doggy paddle).  That's really the way to sight during a race if you can't see enough breathing on your side.