When you're dealing with two high-end, respected phones, it really comes down more to personal preference, although there are some important factors to consider. You still need to procure an invite to order a OnePlus One, although that task is gradually becoming easier. Also, the One comes with Cyanogen preloaded. The removable battery and SD card on the G3 may also be important to you (they definitely are for me). Otherwise, the two handsets are extremely similar spec-wise, apart from the 1440p screen on the G3, which comes with its own benefits and caveats. You really cannot go wrong with either.