FlashChat
A paid chat script which costs $5. Known for masterful integration and good support. Not to mention that master coder Paul M has issued several mods to help increase its functionality with vb. Supports a Module Pack which adds a radio tuner, mp3 player, banner manager, announcements, and a/v chat.

AmfiChat
A paid chat script which costs $5. Less widely used than FlashChat, it comes from the same company. A low-nadwidth chatroom which has a similar feature set to flash chat, with some more server intensive ones removed. Much sleeker interface.

Userplane
An advanced chatroom system which can function as a stand-alone app or integrate with a number of other programs, including vb. Has 3 core components:
Userplane Webrecorder enables users to record and share audio/video messages, Userplane Webmessenger provides live text and audio/video instant messaging, and Userplane Webchat. Free with ads, or very expensive without them.

Real Chat
High end commercial chat software whose price ranges from $495 to $1,495. Includes private chat, session moderation, integrated banner ads, and more. Rarely used, but looks quite professional.

SigmaChat
Both free and paid versions available. Cost ranges from $0 to $135 per year. Features depend on cost. The free package includes such features as: audio support, emoticons, word filtering, and so forth. vB integration though is supposedly less than great. The top tier package includes such features as: transcripts by email, advertisment engine, flood control, enhanced banning, and more. The two top packages (Platinum and Enterprise) supposedly have great vb integration.

123 Flash Chat
Paid ($200) flash chat system which integrates with vb. Features include: A/V chatting, banner rotator, moderation, log system, and more.

Parachat
Not specifically made for vB, but can be made to integrate. From $0 to $155. Features of course vary. Included in the higher end packages are: Integration with db (in otherwords designed to work with vb), transcripts, moderated events, and more.

Pending Release:
vBChat (Updated from 3.0.x)

And then there are a number of irc based options:
PJIRC
IRC Manager
ABD IRC
vbXirc

Apparently, Digitchat integrates with vb as long as you use this hack, but I've not checked.

Undoubtly there are other chat systems, but they don't play nicely with vb and can't share a db.

But the question at hand is this: Of all of these options, which is best? Why?