The 7-30 waters is a more verstile cartridge that was designed and created for the purpose of hunting. The 300 whisper was desinged to be used with 250gr bullets fired at subsonic velocities from suppressed machine guns and bolt action rifles. The fact that it will perform on game was an added side benefit. The increased case capacity and higher velocity makes the 7-30 a flatter shooting round, should you entertain ideas of shooting at longer ranges, and it will push lightweight bullets for varmint hunting/plinking at quite high velocities. Is one a bunch better than the other at 100yds? Probably not, but the 7-30 is more versatile. Also, while it is hard to find, it is a factory round and there is a lot more data for it than the Whisper.
If you decide to go with the 7-30, here are a few bullets I had good luck with in the 7mm TC/U and 7mm BR, which are a little slower than the 7-30:Sierra 130gr Single Shot Pistol bullet, Nosler 120gr Flat Point (deisgned for the 7-30 using the rifle). I used the 140gr Ballistic tips at one time also for tremendous accuracy, but I don't know if the bullet has been changed since then to make them more suitable for rifle velocities so I can't recomend them. Both the Sierra and the Nosler I mentioned will open on deer from a 7-30 Waters, for under 100yds the Nosler would be my first choice.