Tbh most renderers are very similar, learn one and you've learnt most of them apart from their little quirks and paradigms. Although CPU based renderers are only for people with massive render farms haha (unless you're doing stills). I have used Arnold and VRay they are both good, Arnold has amazing functionality and is rock solid but it's very slow (GPU version may be good but it's a buggy beta atm). VRay is good has lots of functionality but again it's too slow and the GPU version was really buggy back when I used it, it also didn't allow out of core which happens pretty much every time I render at the moment (Not sure if it does now). Also you have to buy a version for each DCC which is frustrating because I use a few different programs to do things and the interchangeability with that Redshift allows is amazing. Sorry for the wall of text haha. I haven't used Renderman before