TTS-1 is just great for making midi sound reasonable from the get-go. I have a 3 piece cover "band" (2 guitarists and a lead vocalist) that has me make them karaoke style BG tracks of drums, bass, keys and whatever else is missing to play to when they play the local bars.
They buy pro midi tracks and have me create the backing tracks with my softsynths. When they send them to me via email, I open them to preview with Media Player and they sound like ass. I load the whole file with TTS-1 in the studio and the quality immediately goes way up. Then, I replace a part at a time with the more natural sounding softsynths and tweak the controllers to get the most "real" sounds I can get. Thankfully, the midi files they get are usually pretty well done so there is not a lot of mechanical sounding stuff like Band in a Box outputs to have to tweak.
For strings and bass I usually go with SI as they mix so well but often find I keep a TTS-1 track or two in the mix as well when things get busy.
Now, I really never got into Drop-Zone or RXP, just never really understood them and did not have any projects that I could not complete with the tools I already understood.