I've owned 2 Explorers with SOHC V6, one with the OHV V6 (years ago) and have one with a V8 now. I really love the V8, but it's a pig on gas. Got better mileage with the SOHC for sure. The SOHC is a very fun engine, but you've got to make sure all the TSB work has been done on it (timing chain stuff). Otherwise you'll end up with lots of nagging issues that will cost you $$$ to fix (they used to fix it all under warranty and an extended warranty). Once Ford got all those bugs out, the SOHC is a superb engine. Just take care of engine and tranny with regular maintenance and it will take care of you. Yes, the V8 has a tried and true engine and tranny, but it's really not that cheap to operate (to me anyhow). I've heard you can get 20 mpg, but I can't comment yet because I haven't done any major road trips yet. I get 12-13 in the city right now. I got better than that with my SOHC for sure.
They're both great powerplants. One advantage to a SOHC equipped Explorer is that you can switch to 4-lo, 4-hi, and let the car decide (Control-Trac). Some models have true switchable 2WD. The V8 is full time AWD which contributes to the poor mileage. It does stick to the road like glue though. I love the way it handles in winter so far. Mind you, the 4Lo on my old Sport got me out of a few tough situations so I will miss it.
You won't go wrong with either engine/tranny, IMHO.