In your opinion what are the best rendering softwares?
From what I've heard there are plenty out there, we've only really tried Solidworks' Photoview 360 and Keyshot. Both are really good. Photoview 360 has the option of decals you can apply on your models otherwise we'd use Keyshot with everything else, it does a great job at producing photo-realistic renders. From personal experience we'd say keyshot will run on any current PC.
It has to be 3D's Max and Maya for outstanding visual effects but one small problem with them software's are the interface and the time it takes to set the sense up then you render it out only to find out it was not the effect you are looking for. On the other hand you have Keyshot - My opinion the best there is on the market for someone that does not know much about materials lighting and everything else you would need to know to produce a great render it also has the benefit of the interface being one of the most user friendly I have ever come across in any render software. The speed that you can get that perfect render from and the many great quick tips and tutorials Keyshot has on there web site. If you were to put your money into anything in my opinion Keyshot it as the top of the tree.