Both MR and VR are very good. If you can, I suggest trying out both of them.
Mental Ray ships with Max, it's easier to use because of the frame buffer controls and is more intuitive. Because of this it produces better quality renders at much higher speeds. It also uses scanline materials at no additional render cost, and interestingly enough it is almost completely interchangeable with the unsung hero of your question- quicksilver. Quicksilver renders using DirectX, meaning it can use any modern graphic card to render almost at mental ray quality level tens or hundred times faster. Lastly, iray. Like mental ray, scanline and quicksilver, iray also ships with Max. It is mental ray ported to work on dedicated nvidia CUDA technology. It also uses GPU, but produces photorealistic, true mental ray quality images at faster speeds as it uses both CPU and GPU to work. It is however limited to GPU video RAM so the scenes iray can handle are limited to automotive and arch viz at the moment.
Vray on the other hand is perfectly capable renderer well worth your time. More so if you're in archviz bizz where it's defacto standard. It's a lot more trickier to properly setup, but allows for greater control once you master it. Vray also comes with Vray RT. Vray RT is to Vray what iray is to mental ray- a Vray port to work on dedicated nvidia CUDA technology.
As if nvidia didn't get enough exposure from my post, I'll end this part with- Max prefers nvidia cards in all price segments so you're always better suited to choose an nvidia card over AMD, even if you don't plan to use either iray or Vray RT.
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To student asking about dell or hp- get neither. They are Apples of the PC world. Get a dedicated desktop and ask on a tech forum to help you select the parts that fit in your budget. Try a site like tomshardware.com. You'll find many helpful and knowledgeable persons to help you.
You'll get up to 50% faster computer at the same price point. Ask local hardware service to assemble your parts into a computer. You'll get maximum warranty, local, friendly hardware service if anything should go awry and best of all- you get best performance for your money.
All this unless you need a laptop. They suck, are overpriced- but are mobile and no desktop can give you that. If you can, always get a desktop. Price/performance difference is staggering- esspecially for a normal student price range.