We have used and are currently using all the solutions you mention. They all do the job of connecting and answering customer support questions. If cost is the mitigating factor we offer an in house support solution to our clients at no charge. Our Support Cloud includes FAQs - ticketing/email - and live chat. You can see a live implementation here http://support.atari.com/?/Knowledgebase/List
I have worked in support for over 10 years now and used Salesforce, Zendesk, Zoho Support, Vantive as well as an in house solution and I found that these favour the larger enterprises rather than an SME.
This is one of the things that lead me to create CloudSPRT, although I currently haven't created a Voice Center integration I would love to arrange a quick call (either VOIP or Telephone) to understand your needs and also how I can improve CloudSPRT.