I've sat through the medical research side of things:
- There is no replacement for your real original hip, a good surgeon will get it down with precision, but it does not flex the same way, does not conduct heat the same way etc.
- If you do need it done, get a good surgeon, it may be routine, but if they cut and file too much from your leg bone you will have continuous problems. Your body does not adapt to the difference.
- Make sure you get the latest technology, talk to your doctor. In the US metal-on-metal is no longer FDA approved, but it's still done in Europe, Canada and other socialized medicine systems because of its low cost, if you live there, you may want to consider private insurance or taking a plane ride to the US.
Plastic likewise has issues with buildup of plastic shavings. Full ceramic is currently the gold standard and there are some carbon fiber options in development. There are also some procedures that have started using more bone-preserving procedures, this may or may not be applicable, but if your doctor doesn't know about these options, or tells you they're unnecessary, get another doctor.