What are the options for entering Thailand for a short term stay with a visa waiver or SETV?

My opinion:

1. Get, and enter, on the visa that best meet your needs. If you are planning on a vacation where you will enter, see things, and leave, select whatever visa/ extension of stay that gives you the longest time. If you are planning on converting the visa/ extension of stay to something else, try getting that specific visa before entering.

2. The last day they are selling the 45 day visa exempt is September 30; after that you will be stamped in for 30 days (I don't know what "soon" means).

You are right that there's very little difference since they extended the visa exempt to 45 days to account for ASQ. The only advantage the TR visa has now is that you get an extra 15 days to get your new plan sorted. Almost all change of visas in the country require you to have at least 15 days left when you apply, so this gives you a little more breathing room. But if you get to work as soon as you're out of ASQ, you should have plenty of time using either method.

Visa exempt ot tourist visa. Don't have anything to do with the STV!