I've tried a few of them at this point, and I still think Jeannie is the best. Voice recognition is more than just surprisingly accurate. Also her capabilities to "improvise" and understand what you mean are quite impressive. With Vlingo I tried asking "Where can I get some chicken wings around here?" No results found, google searched it for me which gave a few links that would probably help me out. With the same question, Jeannie, however, opened up Google Maps and placed markers on several local establishments that sold chicken wings within a 10 mile radius, which I could simply tap and either call, get directions, or in some cases see a menu/hours. Also, she'll play 20 questions with you.
Pretty cool if you ask me.