In my opinon the three best weapons in the game go about something this, in order.
1)Small Chainsaw
2)Mega Buster
3)Laser Sword
Although the Small Chainsaw is not as powerful as either the Real Mega Buster or the Laser Sword. The Small Chainsaw achieves greatness in two categories that no other weapons can touch.
The first of which is its availabilty, both the Real Mega Buster and the Laser Sword can take hours of boredom and frustration and are overall hard to get. While the only thing you need to do to get the Small Chainsaw is kill Adam the Clown in the "Out of Control" scoop that appears near the beginning of 72 hour mode. The easiest and funnest way to kill Adam is to simply grab a Katana(There are some in Ripper's Blades in North Plaza, and one hidden on an awning in Paradise Plaza. To get to it simply jump out the one of the far left windows of Roastmasters onto the yellow awning.)and go hack away at him, he should die in just a few hits.(If you are low level and dont have enough health to do it, just grab a few orange juices or wines before you fight him.)
When you kill Adam grab the small chainsaw he drops and BEFORE stoping the ride, hack your way through to the book store there and pick up the Criminal Biography book there, you will need it later. Then go stop the ride and Brian will appear, after the cut scene there will be another small chainsaw on the ground, pick it up. Then follow Brian to the bathroom and he will show you a shortcut to Paradise Plaza. Take it.
The second category is durability, although both the Real Mega Buster and the Laser Sword have a huge durability limit of 300 hits. They hail in comparison to the Small Chainsaw, after we've made some modifications to it anyway. If you read the Criminal Biography book you probably noticed that it gives the Small Chainsaw three times more duribility. Normaly, (without any books) the Small Chainsaw has a duribility somewhere in the realm of 75 hits, which is high, but not high enough. With the Criminal Biography book however it jumps to about 225 hits, better, but still not high enough. But if you go to the larger bookstore in Paradise Plaza, (the one behind the glass) you will find a book called "Entertainment". With this book the duribility of the Small Chainsaw leaps to an impressive 700 hits, but STILL not high enough. In the same bookstore, near the counter, you should find the third and final book, "Engineering". With this book the Chainsaw's duribility elevates to an invincible 2000-2500 hits. If your at a low level this might take up your entire inventory space. But don't worry, with the incredible hacking power of the Small Chainsaw you won't need anything else, no other weapons, not even extra health. Even if you only have one bar of health left. You should be able to hack your way to the next health with getting hurt.
With this new invincible Small Chainsaw of Death you should be able to kill any pyschopath with incredible ease just by running up to them and whacking them 3-5 times.
Warning: In the fight with Larry in "The Butcher" Scoop, bring health. For he deals huge damage with his super move(about 3-6 bars)
Note: The Small Chainsaw does respawn, in the same place you got it the first time.
Note: If its starts to flash don't worry you still have about 600 hits left before it breaks.
Sorry for the novel, But I hope it helped you out.