Blaser R93 Tactical – ★★★★★ Rifle
YZ personally promised she would be good, so she is. Really nice stats, including the highest accuracy stat of all rifles. The skill seems odd, being a two-parter but she does way more damage than it seems, and when her skill pops off, she pops off. The mix of rate of fire and firepower buffs is bigger than it seems (the stacks are multiplicative with each other), and she ends with a significant approximate DPS increase of 86% with all three stacks of her buff and her firepower buff active. Even when her skill is not active, she has very good uptime versus bosses and other high HP targets due to the passive effect. Because of her nature, she can slot in with almost any other rifle and benefit from whatever handgun buffers you want to use.
Note that the existance of a passive means that in moments where no skill is up, R93 will continue to build an advantage over RFs without them. So while on first glance her numbers seem relatively small, she's actually incredible compared to other RFs. Also remember that buffs are multiplicative. 1.4 * 1.1^3 = 1.86. Also note that this is an approximation due to how ROF and frames work (the 'frames per attack' reduction from ROF may vary depending on the current ROF even if the ROF gain/decrease is the same).