First off, the Ambit 3 is available in Peak and Sport edition, I’ll use the Sport edition for this comparison as I feel it’s the better option for a triathlete. The Peak is the better watch, but if you swim, bike and run (or any of those by itself), the Sport edition is all you need.
The question which looks better is always personal, but with the Ambit 3 you have at least four options in colors, where the Polar is available in black and blue.
Both watches support bluetooth sensors, Suunto swapped from ANT+ to bluetooth since the Ambit 2. So if you’re upgrading from an earlier version, keep in mind that your cadence, power heart rate and other sensors may not be compatible. Maybe a miss from Suunto to switch sides, maybe a safe bet considering all the new companies coming out with cheaper, more versatile, and ‘open’ sensors. With open I mean sensors like the Tickr X from Wahoo Fitness which actually has an API to allow other developers to better integrate or support the sensor. This is important as, from what I gathered, Garmin has it’s own methods of sending some data (like vertical oscillation and ground contact time) over ANT+ and doesn’t allow other members of the ANT+ Alliance (including Suunto!) to use this. So an open protocol is good, now let’s hope for a standard and firmware updates all around.
Where weight isn’t a factor I would count in when buying either of these, the Ambit is seven grams heavier than the V800: 86g vs. 79g. Battery wise, the polar lasts about 50 hours and Suunto stops after 25 hours, however, if you upgrade to the Peak you get 50 hours of battery life too.
Both watches can syncronize your activities using your phone’s internet connection and Bluetooth 4.0. When paired, the Suunto also has phone notifications of texts, calls etc.
For your pool sessions, both watches support nearly identical metrics, they can both record heart rate, stroke type, swolf, stroke count, pace, etc. And you can set the pool length to match where you are. The difference here is that the Suunto supports an drills-mode, however, I wouldn’t be surprised if Polar adds this with a firmware update as it has added all the swimming features in November 2014.
For open water swimming, the Suunto is ready too, but Polar plans to release the open water metrics via another firmware update in March 2015. If water resistance is of importance to you, the Polar has a 30meter vs. 50 on the Suunto (and a 100m for the Peak).
Not much to say about the bike here, both watches can give the same metrics and support cadence, heart rate and power sensors.
Similar to cycling, the watches are nearly identical, both support heart rate and give you the expected metrics you want to see. For your running cadence, the Ambit 3 can derive this from your arm movement. But neither give the data for vertical oscillation nor ground contact time which you can see on the Garmin 920XT.
The Suunto has no race predictor.
If you like to set out in an unknown area and follow a gps track, you can do so with the Suunto. Create a track on your computer and upload it to your phone. Polar has similar features, however you can only use pre-made tracks, and thus not something made by yourself or a friend’s past track.
If you’re interested in the outside temperature, Polar actually records it in the V800, Suunto’s Ambit 3 only supports this in the Peak edition.
I list and update price from different stores, giving you the cheapest option, depending on where you’re visiting from. I generally advise to buy watches with their HRM’s, as usually a bundle pack is cheaper than buying separately. And for these watches, to record heart rate while swimming, you need the bundled HRM strap (unless you already have that exact one).