Ok, here's the deal. The slide is your familily, the enharmonics (c & f) are your friends. Due to the unique layout of a chromo. it is very sensitive to how the notes are LAID OUT. The key is unimportant. Because all the notes are there.
Now one might think that playing something IN C ON a C would be easiest. Nope, not always the case. OR one might surmise that if they wanted to play something in Eb that they would find an Eb TUNED chromo easiest. Nope again.
Most tunes are written with no consideration to how they would lay out on a chromo. SO, between the breath switching and slide switching one has to find the best way to play a tune.
This means studying the tune and the way notes FOLLOW each other. Do they require a plethora of breath switching? Not so good. Do they require a lot of slide switching? Well, that's a bit better.
Ironically some of the nicest tunes actually fall better on a C chromo even though they are NOT in the key OF C. This is because the critical notes, And all tunes have a few, may land on a draw note. Draw notes are more conducive to 'milking'. Examples? Ruby, The way we were, etc. are in D. I happen to use a C chromo. BUT you could also do a Richard Hayman and use an A chromo played in the key of F. You would STILL get terminal sound of D. Except it might sound a bit different.
So what IS milking? It's drawing or pulling on a note to accntuate a mood. I can play the same tune in different keys and get dofferent moods simply because of this uniqueness. Sometimes the result is magic. Sometimes it sucks. BUT with the support of your family (slide), and friends (enharmonics), wonderful choices are possible.
Jose Brachemonte