Best Phone For Fitness

Going forward, I am considering getting a device based on fitness stuff going forward, so that means Android or iOS. I am considering getting the S5 Mini or maybe, just maybe (possibly) getting an iPhone. I am making fitness a cornerstone of my life going forward, so far I have been weightlifting at the gym and bench press almost 250 lbs. (max) and I can leg press nearly 400 lbs. I have really gotten better in shape and I am going to start running soon as well, and I need a device that is fast, small, and compatible with plenty of fitness stuff. What do you guys suggest that I take a look at? (I am discounting the iPhone 6, as it won't be that small).