Depends...
If you are planning to use General Midi, HALion Sonic 3 hands down.
It has a dedicated GM mode which accepts program/bank changes. I am 99% certain ST does not have that option.

Also something to consider. Halion has a live support, so if you get lost there are ReAl PeOpLe who actually know their stuff and they will assist you and even do a walk-through even if your purchased product long ago. I find Halion sounds very usable. They have a lot of good quality standard instruments and modern synths that comes with the package. Good balance.

To me, GM mode was the selling point., but I am very happy with quality of instruments it offers.

P.S. I have ST3 laying around on a backup hard drive. I got it cheap, used it on a few tunes and put it aside.