Simplicity-
If you want to hunt deer with your 870, use a rifled barrel with a cantilevered scope mount if you can afford it. This is usually a rock-solid set-up which enables you to switch barrels easily and without losing your sight-in. I have a Hastings barrel for my Remington 11-87 that has worked very well. Much cheaper is a saddle mount, but you'll lose your sight-in if you take the barrel off to clean it (it'll never go back on exactly the same each time). I have a B-square mount and Leupold scope on my 870 with a smoothbore slug barrel (the scope does not sit too high), as a dedicated slug gun; I clean it with the barrel in place so that I don't have to sight it in all the time. This set-up has worked great on deer, as well.
The other gentleman might have had a good experience with rings that clamp onto the rib, but I have not. I tried a scope mount that clamped onto the rib of my girlfriend's 11-87 - there was no way to tighten the screws enough to make it stay put. It moved all over the place, scratched her rib, and got her all mad at me for trying it (got my money back for it, from Brownell's, I think)