I do not have a recommendation for you but I can tell you what I do not like. I got a nylon "tactical" sling for my 870 and it is not something that I would use on a combat gun.
When I'm in a hurry to handle my 870, the sling can easily get between my support hand and the pump handle, rendering it almost impossible to rack the slide. They may work OK for semi's but I would never get one for a pump gun.
I am looking for a nice stiff leather sling that I can use to carry my SG and yet not worry about it flopping around and getting in the way.
Check the Cabela's online store. They have quite a nice selection of inexpensive slings.
Good luck,
Mike
Edited to correct spellling.