Garmin 310 vs 910

There are so many GPS options out there now that you really have to ask yourself what is important to you. 

It's like buying a house.  You make a list of the must have features like a garage, 3 bedrooms, etc. Then you find the model that meets your criteria. 

You don't want to pay for stuff you don't need.  For me, I know I have no interest in heart rate monitoring so I cross that off the list.

I like to keep it as simple as possible.  For a while, running was my main focus so I used a Garmin 110.  Just the basics but that's all I needed.  I use the Garmin 910xt now because I do a lot of open water swimming and the pace/distance is excellent for that.  I also like to see my ride profile which includes an elevation chart and elevation gain.  

It is a personal opinion.  I just bought a Garmin 910.  The reason?  Well my last Polar lasted 10 years.  The one prior to that was 12 years old.  I know I will use this till it dies, so I decided I'd pony up the extra money because I might regret not getting the best later.  If you think it is something that you'll replace in a couple of years, then choose what fits your budget.  But like buying a new bike, you don't want to regret not getting what you want for only a couple hundred dollars more.

Just my $.02.

As some others have suggested it depends on what you want.  The features are what will determine what you want.  I have 910xt and I will say it is great piece of equipment.  However I also have a Garmin Edge 500 for the bike.  I don't use my 910xt when I am just biking.  I had a 210 that I replaced with the 910xt.  My wife had a 305 which we recently replaced with a 910xt.  I know lots of garmin devices.   I am somewhat of a data junkie, and I don't like going for a ride or run with out by pace and HR info.  Here are my thoughts.

If you are just going to use it for just running and HR, then get something like the 210.  Cheaper, smaller and does what you want it to.  However, if you are data junkie and want to track your swim workouts and/or have easier brick data then the 910xt may be worth it.  Or if you want just one device and want to track your entire race then the 910xt is the bomb (even does your T1 and T2 times).   However, the quick release and bike mount are not my favorite for everyday riding and I don't like not having the information in front of me while on the bike (looking at my arm is a pain to me...hence the Edge 500).

The biggest difference to me between the the 310 and the 910 is the true waterproofness.  Don't get me wrong the swim metrics are nice but I am weak swimmer so I get less excited about that info.  I also think the the drastic reduction in size is a big plus.  The strap is much more robust on the 910 (know of a couple of people who lost 310 in the swim because of crappy straps and also a couple that failed because of water).  I am not too familiar with the 310 battery but the 910 battery is 100x better than the 310 and also better than my 210. 

The automatic wireless sync with garmin connect is very slick and the ease of use with training peaks is nice also.  The 910xt is expensive....I personally think the only reason you would want to spend the money is if you are going to use the HR, pace, power, cadence, etc. data that the device tells you.  You may want to consider looking on ebay for one of entry level GPS watches with HR and pace or even the 305 (which would give you bike info) and see if you find in the information useful. 

I just started using a GPS watch a couple months ago.  I got a used 305 for about $110 on eBay, then bought the bike mount with quick release strap and the cadence sensor.  It works great for the run and bike, giving me data I didn't have before.  Simply knowing my pace and knowing when I have slowed down and need to speed back up is immensly helpful.  The cadence is also very helpful on the bike since I can shift to keep cadence releatively level (though I apparently did this pretty well be feel without it).  I don't use it much swimming since it's only supposed to be water resistant for 30 minutes, though I did try the ziplock in the swimcap trick once, but of course my generic ziplock leaked anyway.  Since I can't look it while swimming it's not that useful to me.  I couldn't justify the price of the 910 and figure if I did decide to switch at some point, I can always resell the 305 and get most of my money back.  The only reason I would upgrade is if I wanted a truly waterproof version and longer battery life, but since I don't plan to do a full IM, the battery is fine for me.

The 305 does allow for multisport workouts with transition so you can use it in a race and track everything if you want.  The first race I used it for I just set it for bike-transition-run, and it would worked but I tried to wipe a drop of sweat off it on the bike and inadvertantly hit the lap button which switched it to transition.  I kinda think all these watches should have an option  where they take a double press of buttons for laps and stopping.  That would stop problems from bumping a button.

As far as accuracy on the swim, the one time I tried it in the cap, the route showed up relatively straight, but did have a few abnormal points, which I just deleted.

I like how the quick release mounting works on the 305.  You take the straps off leaving the pins and then it clicks into the bike mount or the velcro wrist strap.  It's quick to take on and off and you don't have to deal with strapping it to the bike mount that the 310 uses.  The velcro strap is much more comfartable than the plastic watch strap and won't slide around.