I have a free version of Cantabile, so that was how I ended up with that. I mostly use Forte - I paid for it, and am quite happy with it. Cantabile works well too, and I believe they have a more robust version you can buy.
I recommend both - I usually end up using Forte, but I do believe either one would do the job.
They both have similar concepts, of allowing someone to load up a virtual synth rack, with VST plugins from whoever, and lets you create as many snapshots as you want, where each snapshot can include any combination of VST synths each playing whatever preset you wish, and any module that is muted gets its memory footprint swapped out, thus conserving resources very well. Additionally, you can do things like decide whether or not an instance of Kontakt reloads samples or not, so if you have an instance of Kontakt with a gorgeous piano sound, you can tell Forte NOT to reload the samples on a preset change, and that makes switching presets instantaneous, because the piano samples are kept loaded up. That feature is HUGELY helpful, and together with the infinite set of presets you can build, with incredibly rich layers and zones and all of that, you get an awesome set of choices that are just about impossible to achieve using any other method I am aware of.
Sonar is FABULOUS for doing what it is designed to do - but live performance VST preset management is a bit cumbersome in Sonar, as there is way too much overhead and time lost when switching sounds, in my opinion.
Bob Bone