For coyote hunting? A fun accessory but completely unnecessary.
I have a railed upper for my 870 that has never been used in the field. A decent tru-glow bead thingy on the front is plenty if you want to get on target faster than with a standard silver bead.
I'm all about the tricked out accessories, believe me, I've had or have them all. (well I've got a lot) but unless your using slugs...you're not going to NEED them.
Now, if you feel that you want them anyway, for whatever reason, a really low profile laser like LaserMax Uni-Max or Uni-Green is my suggestion. The closer to the bore line, the more accurate it will be for the greatest distance range.
I have a 3 rail hand guard on my shotty, tried the laser on that and it's a bad idea. Put it on top of the receiver and its better but still gets in the way of the sight picture. Barrel mounted lasers are a joke. WAY to easy to bump off line.
Scopes on shot guns, are again, in my opinion, only beneficial if you're using slugs.