How do you pick out good LR? I have heard some people say that they have gotten LR that has polyps and other invertebrates on them. What exactly do you look for?
Many factors makes a good live rock. I like large show pieces, plenty of nooks and crannies, porous, coralline algae coverage, plenty of good hitch hikers like sea mats, sponges, mushrooms, etc., tiny critters like copepods and amphipods.
Your Live rock is a base for a natural looking tank and especially a natural bio filter. Try to look for pieces with lots of holes and healthy purple-ish red algae. This make for an excellent bio-filter. Pick pieces that can be put together to create a nice environment.
the critters will show up soon enough!!
As stated there are many things to look for. Here's what I look for though.
Firstly I look for shapes that will make a natural looking reef and rocks with little "dug out" spots that will make good places for setting corals. Then I look for good coloring and growth. Many times you can get some free polyps and stuff on good rock that will thrive once established in your tank. If all these factors are met there is probably a good chance of good and sometimes bad hitchhikers as well. Most times it's hard to find many hitchhikers because they are going to be hiding indide the holes of the rock when they see your hands coming at it to examine the rock. Hope that helps you a little.