For me it has to be the Gewehr M.95. It has the highest ROF out of all the bolt action rifles, a straight pull bolt instead of the rotating bolt-handle, meaning you can stay ADS without zooming out to cycle the next round. It's lack of a sweetspot is compensated by a unique damage model where you put out consistent 75-90 DMG which results in you getting plenty of assists counts as kill and never just an assist.
It's also easily the most versatile allowing you to do well in cqc, mid range and longer ranges once you get used to the muzzle velocity. Not to mention that lightning fast reload.
The M.95 just makes every other scout weapon redundant for my playstyle (I'll still take out the Lebel once in a while). It might be the best weapon I've ever used in BF and I'll never get bored of it.
Enough talking about that though, I've come across plenty of people with 100/200+ service stars on a single weapon and want to hear your thoughts on why a weapon stood out to you over everything else.