I'd say go for Maxwell because even if it's slow you can:

- Have access to a ton of presets (materials)
- Can quickly make physically accurate materials (plastics with real SSS)
- Get perfect lighthing and render settings out of the box (no need to configure things like in Vray)
- You can render your picture for 30min then stop the render and resume the render at any other time

For me all the time you loose in rendering, you gain it back in tweaking your scene and creating your materials

With Rebusfarm I rendered A3 sized images at 300dpi for around 15$ per image with gems and gold materials
(see http://shapenoid.com/Golden-Dreams )

It would cost a lot less for plastics and full HD images