Learn English – “Last thing I’d do is” or “last thing I do would be”

To my ear, the PEU examples are both colloquially natural and accurately described, while the Macmillan examples, although colloquial, are somewhat misleadingly described: things that are happening now might be better expressed as things that have just happened or have just been reported. But that's a minor criticism.

All these examples exhibit the same basic use of will to express habitual or characteristic action. In this sense (like all the modals in all their senses) this habitual will employs its tensed forms, and particularly the past-tense form, to express nuances which may have little or nothing to do with tense. Speaking very broadly,

• Ordinary unstressed uses usually express simple habit—behavior repeated frequently over a long period of time—and tense has its usual significance of present or past reference:

  When he's preoccupied with a problem he will often pace up and down for hours.
  When I was a child we would always go to my grandmother's for Thanksgiving dinner.

• When will or would is stressed, the sense is somewhat different: the habitual action is represented as perversely deliberate. And the tenses are employed somwhat differently, too. The present-tense form generally signifies that the subject currently makes a habit of the perverse behavior:

  She will keep falling in love with the wrong people is rhetorically equivalent to She insists on falling in love with the wrong people.

  But the past-tense form, although refers to a past action, does not express repeated action in the past but represents the subject's behavior on a single occasion as characteristically perverse:

  You would tell Mary about the party ... Even though I asked you not to tell anybody without checking with me, you just can't control yourself around her.

  A: He said it was all Jack's fault.
  B: Well, he would say that, wouldn't he. Nothing is ever his fault, oh no!

(Found it. It's in Unit 491 ("Rather: preference") of Swan's "Practical English Usage".)

Imagine a situation when two persons walk past a café. One of them notices the café, stops and says:

I'd rather like a cup of coffee now!

He is not making a choice among different kinds of drink. He merely means that it would be a great idea to go in so he could have a cup of cofee. He is not expressing his preference to coffee in comparison with red wine, say, because there's no red wine on offer at the moment.

Then our two friends enter the cafe, and he sees a wide selection of different caffeinated beverages, among them a great chocolate icecream cocktail. He says:

On the other hand, I'd rather have that chocolate icecream cocktail.

Now, he is expressing his preference to one drink among a whole range of the available items.