For the most part when you're comparing phones of a similar caliber, you're best to focus on features you WANT in a phone. Oh great the phone can monitor your baby's location and will make a cup of coffee for you, but what good is it if you don't have a baby and don't drink coffee.
What I typically do is make a list of pros and cons for the phones I'm interested in. List them from most important to you to least important. Then literally give a +1 to all pros and -1 to all cons that pertain to my desires. The phone with the highest score I invest in. Now if it hasn't been said, MOST stores have a return policy of 7-28 days depending on the store. INQUIRE, don't assume. Grab the phone and test it out. If you don't like it within that time frame, return to the store and tell them you don't like it and want to EXCHANGE. Saying you want to exchange let's them know you want to continue the service, but just want a different phone.
As long as you don't abuse the exchanging, and the phone is in good un-rooted condition, you're totally fine.
In regards to the phones being water proof, they simply are not, period. They're water resistant, but again, that does not mean you should submerge the phone in liquid to test/prove this. The water resistance is for simple mistakes and mishaps, not underwater video taking.
I personally was interested in the G3, BUT the buttons on the back of the phone were a total undisputable killer for me. That being said, remember, to each his own. But above all, I HIGHLY recommend watching multiple YouTube videos of both phones operating as well as go into the stores and hold the phones and play with them a little (if possible)