I pretty much agree with Nightingale. A lot of people don't understand that the accuracy goes up with the same wpf as you move to lower and lower crossbows. It's kind of like the fluctuation with normal bows, when you add powerstrike, you need more wpf to have the same accuracy you did before you added the powerstrike. It's like controlling raw power, the more power, the more wpf you need to control it. So if you have mediocre wpf, you would be better off with a lower tier crossbow. My thoughts on numbers are slightly different than Nightingale's, but Nightingale knows more about the hard numbers in the game. I wouldn't listen to anyone else's post if I were you.
Summary: Higher tier crossbow = more wpf required for more accuracy/tighter crosshairs. I own a Masterwork Crossbow, Masterwork Heavy Crossbow, and Masterwork Arbalest. I also make use of them for different situations.
Crossbow: Better for a lower pop server, or if your team is getting destroyed. You are able to get more shots off before being forced into melee.
Heavy Crossbow: Your team knows what a front line is and is actively delaying the enemy team, giving you the time to destroy them with your heavier hitting crossbow.
Arbalest: Bring truckloads of tears and salt to anyone or anything you hit with your shot. Usually mounted to the top of a Battleship. Can also watch episodes of your favorite TV series between reloads. Sometimes you only get to shoot it twice in a round. Critical for the other team to counter you.
Crossbowmen are heavily dependent on their team to be effective ranged. Be prepared to be effective in melee, that's why you can be...
Crossbows used to have a chance to penetrate shields... pretty op. I still think they should make crossbows have the 'Bonus against shield' flag...