Everyone will have an opinion of what fits their needs best, and it's always good to hear what others have run into with personal experiences to let each person make their own call on what is best for them.
For me, I love my BellFab mount...my 80 came with the LRA secondary fuel tank and Kaymar rear bumper with swing outs and the tire on the rear. For regular use, which for me is for occasional sunny day cruising or off road trips, I found the swing outs to be a real nuisance overall. While they work well, they do limit visibility and are a hassle when getting into the rear, which I do often if I drive to work for the day. I run with only the front seats, so I still have plenty of space in the rig for whatever I need to carry, plus enough space to roll out the Exped mat for an overnighter without setting up a tent. I've had 2 different tires in mine and have never had any rubber stink inside...I am familiar with it, but maybe some brands or ages stink less than others.
Undercarriage OEM location pros...functions as it should and keeps the tire out of the way. Cons...larger tires to match upsize fit, but can drag for real off road trips, get crusty (I actually sold a spare wheel to a friend since his was ruined from undercarriage storage), dirty as hell when it comes to changing a tire.
Rear carrier/swingout pros...gives you space for the LRA tank underneath, easier access for tire changes, keeps the spare cleaner, looks cool if that's what you are going for. Cons...limited visibility, especially with larger tires, plus I had to re-locate the license plate and light on mine, always in the way for rear hatch access.
BellFab or similar pros...easy access to the spare for me, keeps the spare clean, easy access into the rear hatch (both window and tailgate), keeps the underside free for my LRA tank, still enough space to lay out the XL single Exped mat, very solid mounting with good design and very reasonably priced (compared to a full bumper/swingout system). Cons...some find stinky tire issue, does take up some space inside, especially if you still use center seats (eliminates one 3rd row seat completely).
I'm sure that others may have comments as well on the "list". For me, this was a great solution. Plus, I still have the swing out parts that I can pop back on in minutes and pull the spare out of the truck while leaving the BellFab mount in with minimal space loss if I go on a longer trip or need additional space. I did get lucky and tried the Slee swing arm mount covers that fit perfectly to protect my mount hubs (screw on and have fat o-rings to keep moisture out).
