I bounced a slip-stretched solo vocal track (original tempo: 113BPM, new tempo: 115BPM, stretch percentage: 97%) with the Radius Solo Vocal algorithm selected, but the resulted audio contains 4+ times more artifacts than when I bounced with the Radius Solo algorithm. To my ears the sound quality of Radius Solo is as good as Radius Solo Vocal, so I'm wondering what the point of using Radius Solo Vocal is.
 
Is your experience different from mine? Do you actually use Radius Solo Vocal when bouncing a time-stretched solo vocal track?

Use the one that sounds the best.

Sure, but if many people have the same experience, then maybe there's something wrong with Radius Solo Vocal, and if so the algorithm should be fixed or removed. It's worth asking folks here.

It might work better with individually moved transients as opposed to a full-clip linear stretch or it might just be something about the nature of the particular vocal that you're stretching.  I've mentioned before that I've often found the default Groove Clip algorithm to sound better than dedicated Radius algorithms for full-clip stretching.

Radius used to be sold as a solo product by iZotope, and now they make royalties by allowing others to bundle it. I am not sure of specifics between versions or best usage, but iZotope has been very responsive to emails and may even chime in on this thread if you link it. It would be worth shooting them an email, since that is really their baby.

After my last post, I tried four algorithms (Radius Solo, Radius Solo Vocal, Radius Mix and Groove Clip) on a slip-stretched full-length solo vocal clip in two different projects (I completely forgot to test the algorithms with shorter clips ), and, again, found that Radius Solo Vocal introduces more artifacts than Radius Solo.
 
So, I contacted (icontakted?) iZotope tech support asking why, only to receive a very unhelpful answer (their replies are usually very helpful, but this one wasn't).
 
 
Thank you for contacting us!
 
iZotope Radius allows for independent control over timing and pitch of any audio material while preserving the character and acoustic space of the original recording. Using an advanced hybrid method, it is able to preserve transients and sustained material simultaneously, making it extremely useful for modifying fully mixed performances as well as individual instruments, voices, or other audio sources.
 
If you have any additional questions, please do not hesitate to let me know. Thanks!
 

As for choosing "Groove Clip" for both the offline and online algorithms, it produced unusable results (although it introduced no artifacts IIRC, I could still hear the wavy background noise in the bounced clip). The Radius Mix algorithm introduced no artifacts either, but the tone of the voice changed as if there's a phase issue in it.
 
As I said before, both Radius Solo and Radius Solo Vocal are very good in terms of sound quality, but since BOTH of them introduce artifacts (interestingly, at different points of the song), I think the best practice is to use both algorithms on two duplicated vocal clips respectively and combine the best parts of the two rendered clips.
 
I wish the reference guide didn't just describe the Radius Solo Vocal algorithm as "Best choice when bouncing to track with audio clips of a solo voice." It should explain why it's better than Radius Solo, IF it's indeed better.

You won't really know until you've tried your experiment again, but on shorter clips

True. But if the algorithms are supposed to work better on shorter clips, I think the manual should kindly state that information for new users (so that they won't have to go through the same steps I took).
 
Also, even if it worked better on shorter clips, I'd probably prefer to use the method I mentioned above, since I can never know how short the clips should be until I've tried several times, and also strip-stretching those shorter clips one by one (it can't be done at once, unfortunately) is cumbersome.