A better question would be: 'How many synths should 1 producer try?' And there is the only one correct answer: quite many. This is the right way to find what fits you best. With softsynths it is easier - there are no demo versions of hardware ones. Thus, I'd learn the basics firsthand, using virtual instruments, and refrain from buying "Access Virus or Moog" before you at least can explain what is the difference between them.
Nearly all VST-synthesizers have a demo or trial period so try before you buy. Then, once again, you will know which of them are easier to work with for you. For someone else their interface may be not intuitive or possibilities not the ones they seek but you should see for yourself.
Another problem is that there are many people who are always downloading various VSTi, but don't seem to work on actual music. Thus, it is better to have 1 synth and know it, as it was said, inside and out than 1,000 plug-ins which all do the same and you don't actually use them anyway. So I'd rather you asked yourself which of those synths you tried are subjectively the best, with emphasis on 'subjectively'. I mean, you might have not gathered much knowledge about synthesis yet, but if you had some considerable results with a certain synth - i.e. recorded a track or programmed a sound which is at least approximately sounds as you wanted it to - then learn it deeper from the now on, it seems like it works for (and on) you.
To my view, eventually it is a result that matters - the best instruments are those which inspire you to create more and better music. If you have created loads of good music with one synth only - it is just great. Experienced musicians may need many instruments to make sure they can craft the necessary sound - they know which are better for what etc., - but on beginning stages you don't need much gear or plug-ins, it will only confuse you. You just have to choose a few and move from that point, exploring their sonic potential. For me it is better to use all 101% of what an instrument offers than have a Jack-of-all-trades studio, where you have 10 to infinity keyboards and hardly know what a certain knob or switch is for.