Or: "Learning Your Chosen Synth As Thoroughly As Possible: The Ultimate Option/Solution for Not Blowing a Ton of Money on Myriad Synths and Regretting It Later", aka:
Choose a synth that facilitates expressing your own, individual style as closely as possible. If you haven't learned yet what constitutes your own, personal style, I suggest doing a lot more writing, perhaps using free synths until you can figure it out (not to mention finding out for sure if you really want to do this on a long term basis, even if it's just for you without any guarantee of personal financial gain). Then, exploit that synth's potential as much as possible, progressively becoming more its master as time goes on.
For me personally, once I completely owned Zebra/HZ, I found myself stuck with a ton of stuff I didn't need anymore (including Omnisphere). If I had instead opted to completely learn Omnisphere, it's more than possible I would have felt the same way about that synth. The intensive studying I did with Zebra was hugely beneficial in a musically holistic way as well; not only can you apply what you learned to other synths, but you'll find certain other facets of your writing, arranging, and engineering will have gained from the study. You might even find a free synth that allows you to express yourself in such a unique way that it becomes your "secret weapon". Don't be a victim of the spend spend spend craze, after I did my thing I sold everything but Blue 2, Nave (vst version), and XILS 4. And I really don't even use them much. If you get the right synth (and the four I mentioned along with Omnisphere are all decent to perfect candidates), engrave the user manual in your craggy mind, watch (say) ADSR tutorials until you need toothpicks to hold your lids open, you are going to stand out from the crowd. You'll be the master of one of the most important instruments in the past century. At the least, you'll no longer be among the laptop people whom (though they will viciously deny it, even to themselves), are just treating music as another game.
Ultimately, it's up to you to see in your heart and know both what moves you in music and what motivates you to create beyond yourself. Learn everything needed, then take off with the wings knowledge has granted!