"Which type of nuts ARE/IS the heathiest?" [duplicate]

It seems that people overwhelmingly prefer to write

Which type of nuts are the healthiest?

to

Which type of nuts is the healthiest?

However, type is singular, so why isn't is the correct choice?

Edit if you type these sentences with quotes into Google (phrase search), you'll see that the first one occurs about 3000 times on the web, and the second one basically never.

You could always change the sentence so that it's not so confusing:

1. Which type of nut is the healthiest?
2. Which types of nut are the healthiest?

Note that nut remains singular in both cases, making subject-verb agreement easy. (It's when you use the plural nuts that things get awkward.)