For whatever this is worth, my long (12+) years of research into early Christianity and comparative religion have convinced me that the idea of eternal Hell is false. Now for many other reasons I'm not a Christian, rather more like a Deist than anything, but the original text in for example Matthew 25:47 ("...and these shall go away into eternal torment" in English) does not say that in Koine Greek. The term there is "aionios kolasis," something closer to "age-enduring chastisement." The proper Koine for eternal punishment would be something like "aidios timoria," where "aidios" is basically "unchanging" and "timoria" is what we understand by vengeful punishment, as opposed to the use of "kolasis/kolasin" for "punishment intended to correct behavior."
Combined with constant references to "the second death," as in Revelation's "and death and the grave were thrown into the Lake of Fire, which is the second death," it seems the Bible is preaching Annihilationism. Many of the early church fathers were also Annihilationists and some were even Universalist, and an interesting pattern emerges: the longer the period from Jesus' actual death, and the less Greek (and more Latin) is involved, the more likely endless torture was preached. I seem to recall reading that only the Latinate church at Carthage taught this, while two centers after Origen's tradition and two more descending from Theodore of Mopsuestia were outright Universalist.
Can't speak as thoroughly to Islam, except to say the religion is a hideous fraud. Muhammed knew exactly what he was doing.