It looks like you're new here. If you want to get involved, click one of these buttons!
I've swum 2 half iron distance races breaststroke and two full iron distance races in crawl. I know the crawl was more efficient, but sometimes it's nice to have a fall back stroke.
Do what you want. The important thing is to just do it. Better spend time training and practicing than wondering of you could / should.
I consider myself a confident and relatively strong swimmer (can swim long distances without getting particularly tired).
However, I do struggle to maintain swimming a crawl stroke much beyond 500-600m as I get out of breath. I expect this is due to racing breaststroke as a youth, and therefore I never really developed my crawl.
Whilst I'm not at competing level, I've found that in most open-water swims, the vast majority of the field swimming crawl just can't swim straight and are more of a hazard to other swimmers than breaststrokers.
Case in point, in the Salty Sea Dog 2015 Sprint Tri, the first marker bouy meant swimming perpendicular to the incoming tide, and significant numbers of crawlers ended up 40-50metres down current and had to swim directly into the tide to reach the first mark. With the heads-up benefits of breaststroke, I was able to take the tide into account and over the entire course probably saved 100-200metres in distance over all but the most expert of crawl swimmers, and exited the water around mid-field (with no pre-race training, I might add).
Swim whichever stroke you feel comfortable with, and also take into account the conditions. Breaststroke might just actually be the better, safer and more efficient stroke to use on the day, at least for part of the course.
I've done those Salty Sea Dogs a couple of times, can never work out the tide and always end swimming all over the place, chasing buoys!