Actually, I've used Televantage and VICIdial both quite deeply (including board level diagnostics with dialogic, and expanding systems already in place) and I can honestly say that the differences are not very big (any more).
In older versions of VICIdial (2.04 and earlier) there was a fairly large Gap, in fact. However, that gap was EASILY filled by adding FreePBX to fill in the missing pieces. Then the problem was the Televantage itself was NOT a predictive autodialer, this requires purchasing 3rd party software (which we helped beta test).
By the time you've finished paying for licensing and an installer (unless you're a crazy person like me), you have put in just as much time and way more money with Televantage and your system does NOT do more than VICIdial with FreePBX.
On the more recent side, newer versions of VICIdial (starting with a major milestone of 2.0.5, no need to edit most .conf files outside the GUI), the need for FreePBX to close that gap has dropped. And let's not forget that Televantage still isn't a predictive autodialer and FreePBX is ... well, free.
Now that we are up to 2.4, The Vicidial Group has improved the system to the point that FreePBX is redundant (well, not completely, but it's really not necessary for most applications any more) and there are systems in VICIdial that I never had in Televantage (Although I must say I've lost touch with Televantage since their Lease is what got me THIS job! Thanks Televantage!

)
So today, VICIdial (with the unbelievable capability to add any feature you can reasonably describe to Matt or The Vicidial Group!!) outweighs Televantage by a fairly good margin.
To add a specific function to VICIdial to meet YOUR operational needs may cost a few hundred or a few thousand with The Vicidial Group or an independent such as myself, but try that with Televantage and see how far you get!
Add 10 more agents and see how much The Vicidial Group bills you (um ... nothing?)
Add 2 new servers because you just added 40 more users ... and the money you DIDN'T spend (what $32k?) on Televantage software, dialogic hardware and licensing all-around (user licenses, "agent" licenses, trunk licenses, station licenses ...) will easily pay for as much customization as you can think of.
So from a "user" standpoint (the guy who sits at the desk and says "oooo, pretty") Televantage may be viable. From the standpoint of a Doctor's office that wants to just pay someone to "Drop in a working telephone system" and then "Train Everyone!" and "Tell us how our system works" (since you can't change it), it may be viable if expensive.
But for someone who makes a living with their sales reps on phones with as many customers as possible every day, who has fulfillment centers that WILL change the data requirements without warning ... VICIdial is quite literally the ONLY game in town.
But that's just MY experience.
