Best Coral Glue?

+1 to super glue gel as well
Depending on where or what I am attaching, sometimes I will put super glue on the frag/plug, then a small piece of aquarium epoxy putty, then super glue and then place in the tank where I want. This makes it much easier to attach to some of the uneven rocks.
Super glue gel is the best. Ecotech Marine coral glue works really well, it is essentially super glue gel that's been triple distilled. It seems a little expensive but if you were to buy the same amount of super glue in those little tubes you would end paying more.