Hey, I remeber this thread! Anyway, I find astrology, afterlife and fanaticism to be the most useful, in the order listed. I would much rather have a Hittite priest than a Roman priest. Rome gets fanaticsm, mono, and a bunch of others, but lack astrology, which Hittites do get. I don't think too many will disrepute Egy as the #1 priest civ.
As for actual usage, as Egy, my gold is going nowhere fast, so I tend to build a lot of priests. As with most other units, priests' effectiveness dramatically increases with their number. I used to hotkey priests in pairs, but I quickly ran out of hotkeys and lost track of them as well, so now, I just use a couple of hotkeys on a bunch of priets, and separate them manually in battle. I like to use a bunch of ele archers and a small squad of scythes hotkeyed together to defend the priests. The ele archers do a good job of distracting fire from the priest killers. I also keep one of my large scythe armies nearby fighting, and if a large force of ca's show up to attack the priests, the scythe army sacks them. I've also heard that towers make nice priest guards as well, but I prefer the mobility.
When converting, I usually send out a mass of scythes into the fray, then convert. Sure, the units will be damaged a bit after conversion, but this slows down the target, and gives you extra chances for that 39% to do its magic. If you need near-instant conversion, use multiple priests on a single target.
One thing that I need to do, which I am still a bit reluctant regarding, is martydom. I only do this if I know that my priest is going to die (e.g., a cat ball over my head; a scythe munching on my neck). But I think I should employ this even under safer conditions.
The Egyptian scythe/priest/EA combo is just so sweet. CA's would be a nice addition to this mix, but sorry, my brain just can't handle more than 3+ unit types. I find that this Egy combo can take care of most things except for heavy dual siege and heavy fortifications. In face of either of these, it's time for me to whine to my Hittie buddies.
-joecho