Mr.9 HP: 1011. ATK: 590. RCV: 240 Rank: 1.5/10 Special: 5X damage to 1 enemy. Mr.9 has nothing going for him. Crummy stats and crummy special equal crummy all around.
Log Usopp: HP: 2012 ATK: 938 RCV: 344 Rank: 7.5/10 Special: Delays all enemies by 2 turns and half their defense for 2 turns. Usopp is actually very nice. While he still may be outclassed by Golden Pound Usopp, Log Usopp may be preferred in a few situations when you want that additional attack and to half their defense.
Kaku: HP: 2517. ATK: 988. RCV: 213 Rank: 8.5/10 Special: 1.5X Orb boost for 2 turns. Kaku has decent stats paired up with the awesome Orb-boosting special which makes him a powerful asset to a Striker team.
Gin: HP: 1152. ATK: 792. RCV: 209 Rank: 2/10 Special: 7X damage to 1 enemy. His stats aren't that great... And neither is his special. Try to avoid Gin if you can.
Killer: HP: 2570. ATK: 1449. RCV: -200 Rank: 8/10 Special: Reduce HP to 1 and 100X damage to 1 enemy. Killer is the Striker beat stick. He has an awesome ATK, but his special won't be used to much as it reduces your HP to 1. His power is enough to make up for his flaws though.