Well Claire's handguns allow you to get a laser sighted gun with an extended clip & the SLS 60, her 1st handgun, turns into a Magnum basically with the reinforced frame with high powered rounds. Matilda's upside is that your 9mm DPS is tripled due to the 3 round burst. So it's a matter of if you want eventually 2 handguns, 1 becoming a kind of Magnum, or 1 handgun with triple DPS of its competitor.
Grenade Launcher has more effective range than the Shotgun, but has much less capacity obviously. Plus Grenade Launcher is meant for Lickers, & Shotgun better for dogs. Both are good against zombies in my experience.
Spark Shot is meant for zombies or G Adults, if you get their eye. Claire's best tactic with Ivy Zombies is 1 Acid Round, then 1 Flame Round to finish them.
Magnum vs SMG is a question of semi auto, high damage per bullet, vs low damage per bullet, but rapid fire high DPS. Both can be good for G Adults & Bosses. Just depends on style preference between the two weapons.