We just bought a Crane cool mist humidifier for both ourselves and LO's room. For his, we got one that looks like a dragon, pretty cute - they come in other characters, too. My ped said to make sure you buy a cool mist one and just buy the cheapest one since they are all relatively the same, so that's what we did (after looking at AMZ reviews).
Re: What's the best humidifier?
do you want an air purifier or humidifier?
We have had good luck with the Germ Guardian and with Sharper Image (both are humidifiers, no filters).