Well, I'm certainly not as hard core as the guys on this board, I guess, but currently I'm planning on keeping my 4.0. I think it makes a great rock crawling motor.
Keep in mind that I'm keeping my 4.0. That is not the same as swapping one in. The biggest reason I'm keeping it is because it's there, runs perfectly well, and provides more than enough power for what I want to do. If, however, I had to swap motors for some reason, I personally would probably go the sbc route.
Having said that, the 4.0 is a reasonably powerful, tourquey, trouble free engine. starts all the time. idles like a champ over obstacles. never burns oil. never gives me one once of grief.
the 'idles over obstacles' thing is often overlooked, I think. One person who has a 5.0 ford swap done told me he had a lot of problems maintaining control because even the slightest throttle input sent WAY too much power to the rear wheels. From my motorcycle roadracing days I know that there is such as thing as too much power, in that if you cannot dial in the amount of power you want (between 0 and the maximum available) then the power is not tractable and may overwhelm your available traction.
I find this happens with V8 guys. As soon as they get a V8 they tend to use tire spin a lot more. Could just be cuz it's fun. Anyway, my point is the 4.0 is a very tractable, controllable engine. That's not to be undervalued,IMHO.
Also, less power means less breakage, all other things being equal.
On the negative side, another buddy doing a 5.0 swap discovered that the 5.0 ford V8 is about the same weight as the 4.0 - which means the 4.0 is not saving you anything in terms of weight. And I'm basically unimpressed with most horsepower gaining mods available right now.
All my 2c. And if I had the money, I'd probably go V8 for the same reason most other people do - because I COULD, and because it's FUN.