There is no doubt that choosing between the STs and HT2-TLs is a very tough decision. I chose the HT2-TLs, but I don't think I'd cry about owning the STs.
That said, I am a BIG fan of ribbon tweeters now that I have the HT2-TLs. I thought the tweeters in my B&W 805Ss were good; boy was I wrong! While I'm certain the dome available in the standard ST are good, I can't imagine they sound nearly as good as the ribbons. I have yet to hear a soft dome tweeter I could live with, I couldn't be more impressed with the ribbons used in both the ST-RT and the HT2-TL.
Don't worry about placement of the either speaker. I think this issue is overstated by owners. My HT2-TLs don't seem to require much room at all and based on my in-room measurements, the FR doesn't seem to change much at all. Speaker placement with either choice would most likely affect stage depth and imaging more than anything. But as always, YMMV.
One thing that could differ between the two speakers is midbass performance. My SVS PB13-Ultra never really impressed me with music until I had speakers with more capability from 80Hz to about 200Hz. I have a large room, and I always felt my B&W 805Ss really didn't get the job done. My HT2-TLs are fantastic in this range and I have no more issues in this regard. I can't tell you if the STs would be similar or not, but if I had to guess, I'd say they'd get the job done.
Here is how I'd make the choice:
1. Money: if money isn't an issue, get the HT2-TLs. Why not, right?
2. Midrange: I suspect the midrange performance is ever so little bit better on the HT2-TLs based upon the drivers used.
3. Subwoofer: if you're not going to use a sub for music, I'd vote HT2-TLs.
4. Upgraditis: if you suffer from this affliction, do yourself a favor and get the "better" speaker: HT2-TL.
For the record, I use a subwoofer for music with my HT2-TLs. I tried for some time to not use it, but the bass just sounds better to me with the sub. However, I could easily live without a sub for music with the HT2-TLs.
If it were me, the ONLY choices are the ST-RT or the HT2-TL. I have to have the ribbons.
Good luck with your choice. It's a tough choice, but you can't really go wrong either way.