Wilson Sasha 1 vs Sasha 2.... What songs best convey tweeter differences?

Look at a speaker as a whole. Think about how you will integrate them into your room. Speakers can sound hot, tiresome and shrill for many reasons and tweeter is just one potential culprit. Inadequate amplification that can’t get the bass right, room acoustics with untreated walls and floors and associated equipment are all going to be more influential than the material the tweeter is made from, at least in the case of Wilson speakers.
Don’t overthink it when it comes to the tweeter  

For recordings to use, try Diana Krall “Peel Me a Grape” - good test to see how sibilant the speaker is. It’s also a good track to test the bass.
Keb Mo “I Was Wrong” is a busy track that’s recorded extremely well and is good to test soundstage and how realistic the cymbals sound.

No offence, but to ask for a particular song to hear tweeter differences is a bit of an odd request. Use the music you normally use. I hated the titaniums and think that soft domes are much better. 

My Wilson Audio CUBS have the 1" inverted titanium-coated tweeters. When I first got them, they sounded: "hot" "tiresome" "shrilly".* They were revealing what my system was producing. The cause was dirty power - that injected noise into the electronics. Garbage In/Garbage Out. Now, these same speakers sound sublime. The solution: clean power, quality power supplies (for the source components) and quality cabling. Everybody’s system and electricity is different.

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Even soft dome tweeters and/or ribbons will reproduce distortion (noise) if it’s in the system. Generally speaking, soft dome tweeters will require less coddling over the long run. Titanium-coated may offer a bit more resolution. But there are many variables involved.

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Symptoms of Un-Clean power

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*Many of those negative comments were made before power conditioners stared becoming more ubiquitous.