IMO - As far as synthesizers are concerned, the maker of the instrument is not usually posing the biggest problem.
Inspiring sounds can be programmed in both Live's native instrument collection as well as most popular 3rd-party VSTi you hear about quite often.
It's EXTREMELY beneficial to have a nice idea how to even program a synthesizer and knowing how to program basic common patches when confronted by new synthesizers. Envelopes, Filter response, FX section, Routing and Modulation options are all DIFFERENT in each synthesizer you will come across, I mean Hardware as well. It is vital that IF you are interested in sound design to READ and experiment with what you own and then READ more before you go out an buy the next latest "greatest" thing being promoted into oblivion. You will thank yourself later when you stand in front of a new piece of gear. You will program a basic patch and you will listen to how the envelope(s) respond and interact with the various filter types and THEN you will be better able to decide. Also maybe routing options are important and allow you to get more creative, then you know what to look for. Where can feedback or distortion be placed in the signal, for instance? Or how many operators are there for FM and what modulation options are available? Now I have the patch programmed how do the FX add to it? What FX are available and do they really ADD or Subtract from the patch? Or more practically...Do I get a HEADACHE trying to program a simple patch because the layout of the interface is ridiculously non-intuitive and I lose inspiration while making adjustments? Things to look for.
So are Live's instruments better than VSTi? I say it depends on the programmer and his/her imagination, patience and ability. They all sit in a mix well enough, another advantage to learning how to program yourself. You can make adjustment in the instrument and not only EQ or compression all the time.
Now if youre maybe wondering instead who has the best preloaded patch presets? I don't know really the answer.