[disclaimer: I'm not a dentist]

Gold would be the best for back teeth in terms of longevity and wear
properties. If you're concerned about esthetics, PFM
(porcelain-fused-to-metal) would be most commonly used  for back teeth.
Otherwise gold would definitely be the way to go.

Regarding front teeth - have you actually seen a dentist who said you
need crowns there? If not, there might be other options to restore them
other than crowns (but only a dentist in person could assess that)...
but to answer your question, of course gold could be used on front
teeth as well, but most people are not keen on the bling look. It's
becoming more common these days to use all-porcelain crowns for front
teeth, because esthetically, the result is pleasing (due to no
underlying metal structure). On the other hand, more tooth structure
needs to be removed when preparing a tooth for an all-porcelain crown
compared to a PFM crown (gold requires the least prep). Again, PFM
crowns can be used on front teeth (Captek can be a good choice
esthetics-wise), so this might be a good option depending on your
circumstances.

This is just to give some general idea - you'd really have to sit down
with a dentist who's actually seen your teeth and x-rays and see what
might be the best thing to do in your particular case, because the
choice will depend upon the actual condition of your teeth, your
preferences and lifestyle, other issues such as bruxing or grinding,
your dentist's experiences with various materials etc. etc.

True, forget porcelain as they do crack. Better option is porcelain
fused to metal.

There are other options depending on your bite. As example Kryptonite
works well for Superman.

Joel