Which kind of crown for mandibular first molar?

The answer like most answers is "it depends."  It depends if your smile shows your fist molar. If so, then I would suggest an e.max crown (all porcelain) because it is more aesthetic than full zirconia or gold. If your smile does not show your first molar (this is true for the majority of people) then full zirconia would be best. Another factor it depends on is your habits. If you are a grinder or clencher, then you should sacrifice aesthetics (e.max) for full zirconia. In my opinion I would stay away from porcelain fused to zirconia as the porcelain still has the ability to chip more commonly than a monolithic substance (the others mentioned in my answer). 

The zirconia is superior in strength. Make SURE it fits in your occlusion because if it's off it can cause problems with the tooth above it. Layered zirconia is a bit more esthetic. EMax is superior in esthetics. It's also a great material. We usually don't do gold (due to cost) and I only do a PFM if the patient needs a less expensive option. Anyway, whatever materials you chose make sure you like it before it's cemented! Look in the mirror, compare it to your opposite side. Look at the color. Look at the top of the tooth, the color and groves should match. Look at the shape. If any grinding needs to be done to get it to fit, you can request it be re-glazed at the lab. At the very least, it should be polished. Make sure you like it! It's easy to send ire back to the lab, it's a pain in the butt to cut it off, reprep, two the impression and temporary. ..etc. I do that for patients, but I'm sure some dentists charge for redoes like that. 

Actually, depending on the smile, aesthetics matter greatly on the lower
first molar. The good news is that most
materials can be aesthetic if the tooth is properly prepared. In terms of strength, the same thing applies,
it is all about how you prepare the tooth to receive the crown. On posterior teeth molars, I would go with
Zirconia whether it is full contour or porcelain fused to Zirconia. If strength
is absolutely critical, full contour Zirconia is the choice. There are now aesthetically pleasing full
contour Zirconia crowns that would be more than acceptable for a lower first
molar.