I would go with arbalest, I watch Silveredge destroy with it so I imagine he thinks it the best, and ill take his word on anything crossbow related
I was trying out JesusChrist's Heavy Crossbow. I would say the reload speed to stopping power ratio is the best on the Heavy Crossbow, if you compare them solely on those two points I would say it would be the best choice. However the normal Crossbow gives you the most consistent performance per round. There's a lot more to consider when you're trying to pick which one fits your playstyle. Slots is another thing you have to think about. If you're on a map where you will get plenty of time to use up a stack of bolts, the Normal Crossbow is a better weapon(Unless you really dont care at all about melee). It gives me the option to manually load another stack of bolts when I know I will use them and I don't mind the extra weight. The Arbalest is a great weapon, but you either rape with it or do poorly. The Arbalest is the absolute worst crossbow when the other team charges your position or you have a highly mobile fight, however it is the most devastating crossbow in a single shot. But the Heavy Crossbow is not too far behind.
My favorite is the normal Crossbow, it has the most flexibility out of all of them. Gives you the option to carry 2 stacks of bolts and still have a reliable weapon if you're 1h, or a good 2h and 1 stack of bolts depending on your wpf. It does enough damage with headshots to 1-shot most of the cRPG population even at moderate range and in the hands of an efficient crossbowman, can manage in a mobile fight. The weight nerfs really hurt crossbowmen, its incredible how much slower you move now, this is just another reason to go with the lighter choice.