The answer is rather simple. The one with which you produce great artwork.
Ok, it does look a bit like clickbait but it is a topic which I thought about a lot in the past. And in fact it does not have a single easy answer. So above statement is only partially true.
When I was a student at Bournemouth University back in 2001 there was a big discussion going on between my fellow students. Which is the better one to get a job in the VFX industry: Softimage|XSI or Maya? Both were relatively new at that point. Each had its pros and cons. In hindsight Maya was the better choice as Softimage|XSI discontinued after version 2015. If I would have asked the same question in Belgium I would had the answer: 3D Studio Max. Nobody used Maya in Belgium so getting a job while having excellent Maya skills would have been hard.
It is still a difficult question now that the industry is more globalised and there is more software to choose from. On the other hand my first answer does make sense. Producing nice work gives self confidence and therefor gives the opportunity to produce even better work in the future.
Once you have a good grasp of how 3D software works it is easier to cross over to another package. Certain principles are always the same.
That being said, my choice is currently Maya and Blender (2.8). Maya because it is kind of an industry standard in filmmaking and has nice integration with RenderMan. Blender because it is the best bang for your buck as it is open source and very powerful software. It has even nice features that Maya lacks like motion tracking (Which is actually only needed when combing live action with 3D).
I have been using Maya since version 4 for many professional jobs. Blender is still new to me but looks very promising.