Gavin,
A mate of mind rides a Prophet and loves it. He bought it second hand from a mate who got it as an unwanted pressie from the better half. Didn't like it when he first rode it, actually went back to riding his Giant for a while. Got it serviced and set up properly for his weight and riding style and now says its the best bike he has ridden. Key here make sure it is set up properly when you take it for a test ride. I on the other hand ride a Kona, 03 Kahuna Deluxe, and can't speak highly enough of their quality and frame strength. I ride with all the style and finesse of an overweight thirty seven year old and it has consequently copped a thrashing, it's been flipped more times than I care to remember and aside from incidental breakages (derailer hanger and brake lever) is none the worse for wear. Definietly check out www.mtbr.com for reviews and try www.nsmb.com They may reviews of all the bikes you are looking at.