I've had both since each were released. I have almost twice as many games in Scharnhorst than in Tirpitz. She's just a bit more fun to play. Her guns can be pretty troll to you though...lots of perfectly lined up shots on broadside cruisers result in nothing but a few overpens. Luckily she has the ROF to cover this somewhat. She can be tanky as heck, and can even be highly annoying in tier IX matches as her ROF lets her be quite an annoying fire spammer on tier VIII and IX battleships who stay angled to you.
That said, I also really enjoy Bismarck and Tirpitz. I find them also a lot of fun to play, though it must be said that since Clan Battles started you're going to get uptiered to Tier X matches A LOT. Their dispersion can be annoying, but I find them fairly agile, fast, tanky, and can surprise pop other BBs more reliably than Scharnhorst. They don't have the accuracy and power of the guns on North Carolina/Alabama, but they do have faster muzzle velocities/better arcs.
One fun thing about both Scharnhorst and Tirpitz (and Gneisenau and Bismarck too) is that if the meta ever were to change to heavy CV play, these ships can wreck planes if fully spec'ed for AA due to their heavy large caliber AA suite taking full advantage of the manual AA skill. I have most of my Clear Sky achievements with Scharnhorst while screwing around with an AA build. I had 2 in 3 games, lol.